atmosphericco2glaciationoceanbiogeochemcenozoic--ahagon

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Atmospheric CO2, glaciation and ocean biogeochemical cycle during the CenozoicNaokazu Ahagon (Hokkaido Univ.)

Past changes in the atmospheric pCO2 should be regulated by alkalinity of the ocean

due to the long-term oceanic carbonate system equilibration through both continental

weathering and biogeochemical process. Therefore, increase in orogeny (i.e.,

Himalayan uplift) during the Cenozoic played a major role in Cenozoic cooling by

reducing atmospheric pCO2 (e.g., Raymo et al., 1988). Inversely, episodic volcanisms

triggered global warming by increasing CO2 in this timescale. In this context,variations in atmospheric CO2 and climate during the Cenozoic should be tectonically

controlled as pointed out by BLAG model.

Recently, climate modeling depicted that ephemeral ice-sheet in Antarctica could

appear at mid-late Eocene when the atmospheric pCO2 level was around three-fold of

Present Atmospheric Level (DeConto & Pollard, 2003). Atmospheric pCO2 ranged

between 1000-1500ppmv in mid-late Eocene and then decreased in several steps

during the Oligocene. At the latest Oligocene, pCO2 was equivalent to modern level

and then as low as 200ppmv in the Middle Miocene (Pagani et al., 2005). When such

ephemeral ice-sheet accelerated the increase in alkalinity through continental

weathering and/or shelf to basin transport of calcium carbonate via sea-level change,

the carbonate compensation depth (CCD) was transiently pushed down and then

recorded as Eocene CCD excursions in Pacific sediments (Lyle et al., 2005).

Subsequently, the Eocene-Oligocene boundary marks a permanent deepening of global

CCD by more than 1 km that associated with the major glaciation of Antarctica.

Oxygen isotope record around E/O boundary indicates that duration in development of

Antarctica glacier was only 300 kyr. Theses evidences support strong relationship

between atmospheric CO2 levels and glaciation of Antarctica but the causal

mechanism has not yet understood.

However, CO2 -glaciation relationship in the icehouse world is still matter of debate.

Several results imply that the global cooling and ice growth during the Neogene are

not associated with decrease in atmospheric pCO2 (e.g., Pagani et al., 1999; Pearson &

Palmar, 2000). In contradict to marine proxies, stomatal reconstruction from fossil

plant indicates that the atmospheric CO2 was increased by 1.8 PAL at Mid-Miocene


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warmth (Krschner et al., 2008).

More recently, Lunt et al. (2008) argued that Late Pliocene Greenland glaciation was

mainly driven by a decline in atmospheric CO2 levels during the Pliocene. Because the

atmospheric pCO2 is estimated to be ~400ppmv during mid-Pliocene (Raymo et al.,

1996), only net decline of ~120ppmv to preindustrial level (280ppmv) is responsible for

Greenland glaciation. They used both coupled AOGCM and ice sheet model to assess

the effects on major four hypotheses for northern hemisphere glaciation (i.e., closure of

the Panama seaway, ENSO, mountain uplift and CO2). If the hypothesis proposed by

Lunt et al. is most probable one for expansion of northern hemisphere ice-sheet after~3 Ma, small changes in atmospheric CO2 can control the northern hemisphere

ice-sheet and have impact to future climate change driven by rising CO2 levels. During

Pliocene warmth, North Pacific sediment was characterized by higher opal deposition

due to higher nutrient availability by vigorous mixing with subsurface waters. The

opal productivity was suddenly decreased at the Northern Hemisphere glaciation at

2.7Ma, presumably caused by surface ocean stratification owing to sea-ice condition or

excess precipitation over evaporation (Haug et al., 2005). Such surface ocean

stratification could lead further feedback of declining CO2. However, pCO2 estimates in

the geologic past have still large uncertainty or conflicting results among proxies.

Further improvements in CO2 proxy records are required.

The role of oceanic gateways is still necessary to understand because it affects heat,

water and salt transports among ocean basins. Particularly, in contrast to Panama

Gateway, evolution of Indonesian Passage during the Cenozoic and its effect on climate

have not well investigated by paleoclimate community. Indeed, change in nature of

Indonesian Throughflow in todays ocean can strongly affect global climate. In addition,

switch in source water of Indonesian Througflow from South Pacific to North Pacific

waters could lead cooling of the Indian Ocean and then increase the aridity of Africa in

Pliocene (Cane & Molnar, 2001). Future planning of Pacific paleoceanography should

focus at this point.


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Sedimentology, Paleoceanography

IODP ICDP


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Dec.4-6, 2008, Nasu, Tochigi Pref.

IODP INVEST meeting proposals

Takashi ITO (Faculty of Education, Ibaraki University)

I would like to propose a few scientific views regarding paleocenanographic study for new stage of

IODP. Theses are standing in just scientific point of view without political, technical and financial

problems.

Proposal TI-1) Paleoceanography of anoxic and hydrothermal basins

Objectives

-To reconstruct degree and type of hydrothermal activity through Earth history

-To understand geochemistry and microbiology in anoxic-hydrothermal area-To understand the origin of Precambrian banded iron formation based on comparable study

with modern analog

Significances

-Hydrothermal activity within anoxic environment is very precious, because sulfide phase ofhydrothermal deposits under the anoxic condition will be preserved well without oxidization.

So, we will be able to reconstruct the degree and type of hydrothermal activity with high time

resolution.-In surrounding area of anoxic and hydrothermal basins, processes of oxidation and subsequent

sedimentation of metal are carried out. Understanding of these processes will be a key to

realize the origin of the sedimentary ore deposits, i.e. Precambrian banded iron formation

(BIF) and Phanerozoic bedded manganese deposits.

-The relationship between hydrothermal activity and surficial productivity will also beimportant.

-Geochemistry and microbiology in anoxic and hydrothermal basin is important as theadvanced study of present Initial Science Plan, IODP.

Potential drilling sites

-Red SeaHistory of drilling

-Red Sea: DSDP Leg 23, Sites 225-230 (e.g. Stoffers and Ross 1972)-Red Sea: Many commercial based drilling cores (e.g. Crossley et al. 2007)

References

Crossley et al. (2007) Jour. Petroleum Geol., 15, 157-172.

Stoffers and Ross (1972) Int. Rept. DSDP, 23, 849-865.


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Proposal TI-2) Paleoceanography based on time-space distribution of sedimentary

and hydrothermal ore deposits

Objectives

-To reconstruct paleoceanographic environments based on time-space distribution ofsedimentary and hydrothermal deposits composed of redox sensitive elements, and on their

mineralogical, chemical and isotopic signals.

-To redefine origin of sedimentary and hydrothermal deposits based on the most advancedtechnology and comprehensive viewpoints. Especially, to date the metallogenetic epoch and

to situate the epoch at the paleocenographic timescale in high resolution.

Significances

-The ocean drilling targeted origin of ore deposits has been carried out only in fewhydrothermal ore deposits (e.g. Juan de Fuca Ridge: Goodfellow et al. 1999).

Non-hydrothermal sedimentary deposit is out of scheme in previous DSDP/ODP programs

except some evaporites (e.g. Hsu, 1983). But, in addition to common paleontological and

geochemical studies for sediments, metallogeny and time-space distribution of sedimentary

and hydrothermal ore deposits are important to understand comprehensive sedimentary

environments. For example, shallow marine manganese deposits develop at the oxic-anoxic

interface of a stratified basin (e.g. Force and Cannon, 1988). In addition to direct studies for

anoxic sediments, shallow marine sides surrounding anoxic basins are also a key of

understanding of OAE events-Age determination methods have made spectacular progress. Regarding oceanic ore deposits,

Re-Os methods and Sr-Os isotopes stratigraphy are developing (e.g. Klemm et al. 1995).

Using such new developed techniques, dating and correlation of the metallogenetic epoch to

paleocenographic timescale in high time resolution will give us new perspective.

Potential drilling sites

-Off Groote Eylandt, Northern Territory, Australia-Cretaceous ocean anoxic basin and surrounding area-Okinawa trough-Tertiary Kuroko basin (land drilling)

History of drilling

-Juan de Fuca Ridge: ODP Legs 139, 169 (Goodfellow et al. 1999), IODP Exp. 301-Cretaceous ocean anoxic basin: Many DSDP/ODP Legs.

References

Force, E.R. and Cannon, W. F. (1986) Economic Geology, 83, 93-117.

Goodfellow et al. (1999) Review in Economic Geology, 8, 297-324.

Hsu, K.J. (1983) The Mediterranean was a desert, Princeton University Press.Klemm et al. (2005) Earth Planet. Sci. Lett., 238, 42-48.


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Cenozoic Antarctic Ice History and Establishment of Marine Biotic Provinces:

Biotic response to the Cenozoic stepwise cooling and partitioning of oceans.

Masao IWAI

Department of Natural Science (Geology), Kochi University

Akebono-cho 2-5-1, Kochi 780-8520

Japan

Key Questions:The ecological provinces of the open ocean are principally controlled by physical properties of

the ocean with nutrient limitation. How were the oceanic frontal system and/or stratification

of water which affected by the global cooling established? How those work to the partitioning

of marine provinces? How do the fundamental mechanisms of partitioning of OceanicProvinces differ to those on land? Our understanding to those key questions is essential to the

evolutional biogeography and also important to better understanding of global biogeochemical

cycles.

Target time interval:The Cenozoic has been a period of long-term cooling from the relatively warm and sea-ice-free

Cretaceous and Early Eocene greenhouse to the Quaternary icehouse world, which was

affected by plate tectonic processes such as the break-up of Gondwana supercontinent.Cooling of the polar region led increased contrast of water temperature in both latitudinal and

vertical, and subdivided water bodies. Relatively few records are before Miocene.

Target area:As a case study, the author proposes the latitudinal transect drilling in the Southern Pacific

Ocean. Several DSDP-ODP cruises are performed and one IODP cruise has been planed in the

Antarctic continental margin to reveal the Antarctic Ice History, however, poor core recovery

restrict our understanding of the detail. Also relatively few drilled sites in the Southern

Pacific Ocean restrict our understanding on the regional paleoceanography and temporal

variation and changes of flora and fauna.


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Paleoceanography below carbonate compensation depth (CCD): toward better understanding for

glacial carbon reservoir

(Yusuke Okazaki1

, Yusuke Suganuma2

, Kana Nagashima1

)

1 Japan Agency for Marine-Earth Science and Technology

2 Ocean Research Institute, University of Tokyo

The Earths climate experienced 100 kyr glacial-interglacial cycles during the last million years.

Analysis on ice cores from the Antarctic has revealed that atmospheric CO2 content varies in

harmony with glacial-interglacial cycles. During the last glacial period, atmospheric CO2 content

was estimated to be approximately 80 ppm lower than the pre-industrial level. However, we have no

consensus to explain the lower CO2 content. Because the mass of carbon stored as terrestrial biomass

was smaller during glacial than during interglacial periods, deep-ocean must be a major carbon

reservoir during glacial periods. However, our knowledge on glacial properties of deep water (i.e.,

temperature, salinity, nutrient and carbonate ion contents) is still scarce because of the difficulty to

establish reliable age-model and lack of quantitative paleo-proxy due to the poor preservation of

carbonate (i.e., foraminifer shells) below carbonate compensation depths (CCD). Such deep-sea with

carbonate-free sediments are distributed in vast area of the Pacific and Southern Ocean (Fig. 1). The

Pacific Ocean deep water would have been a major glacial carbon reservoir due to its great volume.

However, there is little knowledge on the glacial Pacific deep water. The Southern Ocean is the most

important area to understand orbital-scale carbon cycle and climate because mechanisms centered in

the Southern Ocean explaining near-synchronicity between Antarctic temperature and atmospheric

CO2 during the termination I, which is not observed in the high-latitude Northern Hemisphere.

We propose to reconstruct orbital scale variations in ocean circulation and carbon cycles in the

vast area below CCD in the Pacific and Southern Ocean by the following strategies.

1. Establishing reliable age model based on geomagnetic field intensity and cosmogenicnuclide (

10Be), comparable with the Antarctic ice-core records.

2. Reconstruction of water-mass properties and productivityemploying silicates (biogenic opaland quartz) preserved in sediments below CCD

Details:

1. Age model establishment based on relative geomagnetic field intensity and cosmogenic nuclidesNormally, age model for open-ocean sediments is constructed by using

14C dating and oxygen

isotope carve fitting of foraminifer shells. However, these methods are unable to adopt for deep-sea

sediments below CCD due to poor preservation of foraminifer CaCO3 shells.

Recent progress in relative paleointensity studies has revealed that open-ocean marine sediments


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record long-term (10 to 100 kyr) secular changes of the geomagnetic field intensity (Fig. 2). These

accumulated paleointensity records has allowed establishment of composite stacks of geomagnetic

field intensity, which has been applied to develop original age models in deep sea sedimentary

sequences. Production rate of cosmogenic nuclides, such as10

Be, fluxes is also largely controlled by

geomagnetic field intensity. Hence, temporal changes in cosmogenic nuclide fluxes recorded in

marine sediments can be used as a tracer for the geomagnetic filed intensity and dating tool likewise

paleointensity (Fig. 3). Further, geomagnetic field intensity and cosmogenic nuclide flux records in

marine sediments are permitted direct comparison with cosmogenic nuclide flux records in ice cores,

allowing us to establish fairly accurate age model even in carbonate-free sediments.

2. Validation for a synthesis scenario by Sigman and Boyle (2000)Among numerous models explaining lower atmospheric CO2 content during glacial period, a

synthesis scenario by Sigman and Boyle (2000) is persuasive (Fig. 4). They suggest that lower

atmospheric CO2 during the last glacial period was caused by changes in water-mass structures with

intensified stratification and changes in nutrient utilization and rain ratio with enhanced aeolian dust

fluxes in the Southern Ocean. In order to examine this hypothesis, reconstruction of (1) water-mass

structure and (2) relationship between eolian dust flux and biological productivity relating to the

wind system change such as the westerly jet axis is required.

We propose that oxygen isotope from biogenic opal could be a water-mass proxy adopt for poor

CaCO3 preservation area. Microorganisms making siliceous shells dwell from surface (diatoms and

radiolarians) to intermediate (radiolarians) and deep (sponges) water. Thus, vertical water-mass

structure can be reconstructed if their oxygen isotopes retain information on water-mass (i.e.,

temperature and salinity) when they produced their shells. Fortunately, the Southern Ocean and the

subarctic Pacific have abundant diatom production, thus we can easily collect sufficient amount of

silicates from the sediments. Eolian dust flux and their provenance can be reconstructed based on the

physical properties and oxygen isotope of quartz in sediments, providing information on the past

wind system. Biological productivity is reconstructed based on various proxies such as biogenic opal,

barium, nitrogen isotope, biomarkers and diatom assemblages. These reconstructed data would be

strong constraints for the lower glacial CO2 model.

Recent paleoceanographic studies are mainly focused on high-resolution analysis from high

accumulation sediments. However, sediments from open-ocean must have recorded unique

information such as deep-water property. We propose that we should pay attention to not only

shallow and high accumulation area but also deep and low sedimentation area and try to seek

evidences toward better understanding for past ocean circulation and carbon cycle.


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Fig. 1. Map of the sediment distribution of CaCO3 content (Sarmiento and Gruber, 2005).

Fig. 2. Synthetic record (Sint-800) with its standard error obtained from the stack of 33 records

of geomagnetic field intensity (Guyodo and Valet, 1999).


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Fig. 3. Changes in (a) d18O, (b) 10Be concentration, and (c) 10Be flux records in the Greenland ice

core during the last 60 kyrs (Muescheler et al., 2005).


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Fig. 4. The modern ocean (a, b) and a Southern Ocean-based hypothesis for reduced levels of

atmospheric CO2 during glacial times (c, d) (Sigman and Boyle, 2000).


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Cenozoic paleoceanography in the North Pacific

Shin-ichi Kamikuri and Isao Motoyama (University of Tsukuba)

[Background]

The North Pacific is unique in the worlds ocean. At present, the North Pacific is the terminus of the deep water

circulation route originating in the northern North Atlantic Ocean and the Antarctic Sea, and the beginning of the

return surface circulation. These old deep waters are nutrient-rich, oxygen-poor and highly corrosive to calcium

carbonate. Passes through the Aleutian and Kuril arcs provide exchange sites for deep waters that exert a strong

influence on the properties of North Pacific Intermediate Water (NPIW) and possibly deeper waters. The North

Pacific includes two major surface circulation systems (the subtropical and subarctic gyres) and an oceanic frontal

zone (the subarctic front), which have migrated over several degrees of latitude on both short and long time scales.

The area is a source of heat and moisture for the North American continent and is one of the most biologically

productive areas of the world ocean.

The climatic evolution of the Earth during the Cenozoic largely reflects a trend toward lower temperatures and

cryospheric development of the polar region in the Northern Hemisphere (Zachos et al., 2001). This evolution

resulted from decrease of atmospheric CO2 and/or increase of poleward atmospheric and ocean heat transport by the

opening or closing of oceanic gateways. Gateways are narrow passages linking the major ocean basins, and changes

in their configuration alter the amount of seawater exchanged between oceans, as well as the heat and salt carried by

seawater. Several scientists have proposed that gradual changes in key gateways (Indonesian, Central American and

Bering seaways) caused glaciations by altering the poleward transport of heat and salt (e.g., Cane and Molnar, 2001).

During the early Cenozoic, open circulation between the tropical Indian and Pacific Oceans was possible through

the Indonesian Seaway (Kennett et al., 1985). During the late Neogene, the establishment of water exchange between

the northern North Pacific and Atlantic would probably have strongly influenced general ocean circulation, and hence

global climate. The open connections between two huge water masses with different temperatures have resulted from

the first opening of the Bering Strait (Marincovich and Gladenkov, 1999). However, how these interocean exchanges

affected oceanic and atmospheric circulation in the North Pacific are not well known.

Atmospheric circulation and its link to oceanic surface circulation and biological productivity are important

components of global climate change (Rea, 1994). The past variations in zonal wind intensity have poorly understood,

because direct evidence for changes in zonal wind strength is rarely preserved in sedimentary deposits. Temporal

changes in the intensity of atmospheric circulation are reflected in size distribution of small eolian particles

transported in equilibrium with the winds. Eolian particles isolated from pelagic sediments will provide us with an

opportunity to investigate the nature and variability of the Cenozoic atmospheric circulation intensity.

Studies of regional opal sedimentation rates of the North Pacific demonstrated significant redistribution of

accumulation rates in the latest early and late Miocene and early Pliocene and suggest a marked change in biological

productivity. However, how this change in opal sedimentation is related to changing ocean circulation as yet is

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[Objective]

Our primary objective is to obtain complete and continuous sequences of Cenozoic biogenic sediments in order to

understand sedimentation, paleoproductivity, oceanic circulation and wind patterns during the Cenozoic in the North

Pacific. Specific paleoclimatic-ceanographic questions to be addressed include the followings:

1. How did the atmospheric circulation on the North Pacific evolve through the Cenozoic?2. How did the Cenozoic mass balance of carbonate and opal burial change in detail?3. How did the North Pacific CCD move through the Cenozoic?4. How did the subtropical and subarctic gyres evolve through the late Cenozoic as a response to increased

global glaciations?

5. What was the nature of the subtropical and subarctic gyres during the Oligocene and early Miocene after theformation of the Japan and Okhotsk Seas?

6. What was the nature of circulations during the middle and late Miocene after the partial closure of Indonesianseaway?

7. What was the nature of circulations during the early Pliocene after the opening of the Bering seaway?8. What was the nature of circulations during the late Pliocene after the closure of Central American seaway but

before the onset of Pleistocene glaciations in the Northern Hemisphere?

9. How did the Bering circulation evolve through the Cenozoic?10. How did the Okhotsk circulation evolve through the Neogene after the formation of Okhotsk sea?11. How do the changes of the surface water circulation affect North Pacific Intermediate Water?12. How do the oceanographic changes in the North Pacific affect biological productivity?

[Drilling plan]

Bering and Okhotsk Seas and Northwest Pacific

Cane, M.A. and Molnar, P., 2001. Closing of the Indonesian seaway as a precursor to east African aridification around 3-4 million

years ago.Nature 411, 157-162.

Kennett, J.P., Keller, G., and Srinivasan, M.S. 1985. Miocene planktonic foraminiferal biogeography and paleoceanographic

development of the Indo-Pacific region. In: Kennett, J.P. (ed.), The Miocene Ocean. Geological Society of America, Memoir

163: 197-236.

Marincovich, L.Jr. and Gladenkov, A.Y., 1999. Evidence for an early opening of the Bering Strait. Nature 397, 149-150.

Rea, D.K., 1994. The paleoclimatic record provided by eolian deposition in the deep sea: the geologic history of wind. Reviews of

Geophysics 32, 159-195.

Zachos, J., Pagani, M., Sloan, L., Tomas, E. and Billups, K., 2001. Trends, Rhythums, and Aberrations in Global Climate 65 Ma to

Present. Science 292, 686-693.


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Estimation of changes in future oceanographic environment based on past oceanic

anoxic events (OAEs)

Azumi KUROYANAGI (Ocean Research Institute, The University of Tokyo)

During the Mid-Cretaceous (Barremian-Turonian), oceanic anoxic events (OAEs)

occurred several times and they were distinguished by discrete beds of black shale

and/or pronounced carbon isotopic excursion. Changing nutrient availability and/or

upper water column structure would be the causes of plankton turnover at or near the

OAEs (Leckie et al., 2002). For example, largest and most heavily calcified plaktonic

foraminifera were seriously affected by the ocean-climate changes associated with

OE1b. In contrast, the deepest-dwelling planktonic foraminifera were eradicated (22%

species became extinct, while 20% speciation rate for a total of 42% species turnover)

during OAE2 which was likely caused by an expanded oxygen minimum zone

associated with elevated productivity and/or by the decay of the thermocline due an

abrupt deep-sea warming event (Leckie et al., 2002).

Global surface air temperature (SAT) has increased 0.6 0.2C over the past

century. The average annual discharge of fresh water from the six largest rivers to the

Arctic Ocean increased by 7% from 1936 to 1999, and the average annual rate of

increase was 2.0 0.7 km3/year (Peterson et al., 2002). The Intergovermental Panel on

Climate Change (IPCC) projects a global SAT rise between 1.4 and 5.8C by 2100.

Thus, discharge from the six largest Eurasian arctic rivers alone would increase by 0.01

to 0.04 sverdrup (315 to 1260 km3/year) by 2100 (Peterson et al., 2002). Freshwater

sensitivity experiments suggested that 0.060.15 sverdrup of additional freshwater

entering the northern Atlantic, after which North Atlantic Deep Water (NADW)formation cannot be sustained (e.g., Clark et al., 2002). Freshwater input and SAT rise,

causing a decreasing of vertical mixing of water column and shallowing of the lysocline

(strong thermohalinestratification). Therefore it would be lead to a deep water anoxiaand changes in ocean circulation, water column stratification and nutrient partitioning

affected a reorganization of planktonic community structure in future.

In general, most fish cannot live below 30% dissolved oxygen saturation, and a

"healthy" aquatic environment should seldom experience under less than 80% of

dissolved oxygen level. Previous studies reported that the relationship between


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foraminifera and oceanographic conditions (temperature, salinity, food availability, light

intensity, water column stratification, etc.) (e.g., Sautter and Thunell, 1989; Watkins et

al., 1996; Kuroyanagi et al., 2008). However, the foraminiferal biological reaction to

changing dissolved oxygen has never been examined from viewpoint of calcification

under low dissolved oxygen level because of the difficulty of observation and/or control

of dissolved oxygen under the modern ocean condition.

Planktonic foraminifera keep records of the upper ocean environments in their

assemblage and individual tests. Culture experiments investigate quantitatively the

relationship between foraminiferal ecology and parameters such as temperature, salinity,

light intensity, etc. (e.g., Bijma et al., 1990). These laboratory studies provide detailed

biological information under controlled conditions, but must be examined for their

applicability to field conditions. In order to estimate the changes in biological reaction

of planktonic foraminifera with dissolved oxygen, 1) culture experiments and 2)

reconstruction of foraminiferal changes in combination with dissolved oxygen during

the OAEs would be effective and appropriate resolution.

[References]

Bijma J., Faber Jr.W.W., Hemleben C. (1990)J. Foraminifer. Res.,20, 95-116.Clark, P.U., Pisias, N.G., Stocker, T.F., Weaver, A.J. (2002)Nature, 415, 863-869.

Kuroyanagi, A., Kawahata, H., Nishi, H., Honda, M.C. (2008) Paleogeogr.,

Paleoclimatol., Palaeoecol., 262, 115-135.

Leckie P.M., Bralower T.J., Cashman R. (2002) Paleoceanography, 17, 13-1.

Peterson, B.J. et al. (2002) Science, 298, 2171-2173.

Sautter, L.R., Thunell, R.C. (1989)J. Foraminifer. Res., 19, 253-267.

Watkins, J.M., Mix, A.C., Wilson, J. (1996)Deep-Sea Res. II, 43, 1257-1282.


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Reconstruction of long-term variability of the solar activity based on geomagnetic field

intensity and flux of cosmogenic nuclides recorded in deep-sea sediments: possible

connections among the climate, sun, and geomagnetic filed

Y. Suganuma*1

, Y. Yokoyama*1,2

, H. Miyahara*3

, T. Yamazaki*3

*1Ocean Research Institute, University of Tokyo, *2 IFREE JAMSTEC, *3 ICRR, University of

Tokyo, *4 Geological Survey of Japan, AIST

Recently, a possible link between solar activity and climate variation in decadal and century

scales has been debated (e.g., Rind, 2002). Moreover, the past variability of solar activity has

been reconstructed by flux of cosmogenic nuclides (14C, 10Be, etc.) recorded by tree rings and ice

core, suggesting their linkage in longer time scale (Beer et al., 2006). However, the variability of

the total solar irradiance over a typical 11-year solar cycle is only approximately 0.1% (Froehlich,

2006), which is too small to explain the observed

climate variations (Foukal et al., 2006). On the

other hand, there are other ways that solar

variability may affect climate, such as a terrestrial

amplifier of the spectral irradiance variations

(Haigh et al., 1996), or an indirect mechanism

driven by the solar activity. The later can be

realized by galactic cosmic rays (GCR) via the

ionization effect in the atmosphere. GCR induced

ionization is the principle source of the ionization of

the low and middle atmosphere and can slightly

modulate cloud formation, which is likely to affect

climate through changes in transparency/absorption/

reflectance (e.g., Svensmark, 1997). Because the

flux of GCR is modulated by solar magneticactivity, this phenomena provides a possible link

between solar variability and climate (1234

in Figure 1).

On the other hand, the flux of GCR is not only controlled by solar activity, but also by the

strength of the geomagnetic field largely. When the geomagnetic field intensity is low, GCR can

more easily penetrate into the Earths atmosphere and then increase the production of cosmogenic

nuclides, such as 10Be. Figure 2 shows that dependence of the 10Be production rate on the

geomagnetic field intensity and the solar activity. In the last two decades, paleomagnetic studieson marine sediments have revealed long-term (10 to 100 kyr) and large-amplitudevariationson the

geomagnetic field intensity (e.g., Guyodo and Valet, 1999). This indicates that reconstruction of


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the past variability of solar activity using the flux change of cosmogenic nuclides urgently needs

correction by the geomagnetic field intensity. Moreover, the variation of the geomagnetic field

intensity possibly affects could formation

and climate, in especially longer time scale

(5234 in Figure 1). However, the

most reconstructions of the past solar

activity have not been sufficiently corrected

by the geomagnetic field intensity and they

usually focused only on the relationship

between solar activity and climate.

Therefore, a highly accurate reconstruction

of the past solar activity using cosmogenic

nuclides corrected by a high-resolution

geomagnetic field intensity record is needed

in order to understand the relationship

among the climate, sun, and geomagnetic field.

Here, we propose that the possible connections among the climate, sun, and geomagnetic

field should be assumed to be one of the main challenges in the next IODP phase. Although,

conventional piston coring strategy is limited by time coverage especially in case of higher

sedimentation rate, new drilling plans in IODP are able to recover long-term sedimentary records

with high sedimentation rate in order to provide high-resolution cosmogenic nuclides (in this case10Be) and geomagnetic field intensity variability. Because very limited input of terrestrial

materials is needed for cosmogenic nuclides analysis, preferable drilling sites are thought to be

open ocean area except the west wind belt zones. Moreover, equatorial zone is suitable for this

study because of higher sedimentation rate originated to high biological productivity. These new

drilling plans in IODP will arrow to reconstruct the long-term solar activity in high accuracy that is

needed for test the possible connections among the climate, sun, and geomagnetic field.

Haigh, J.D. (1996) The impact of solar variability on climate, Science, 272 981984.

Beer, J., M. Vonmoos, and R. Muscheler (2006), Solar variability over the past several millennia, Space Science Reviews, 125, 67-79.

Rind, D. (2002), Climatology - The sun's role in climate variations, Science, 296, 673-677.

Svensmark, H., and E. FriisChristensen (1997), Variation of cosmic ray flux and global cloud coverage - A missing link in solar-climate

relationships,Journal of Atmospheric and Solar-Terrestrial Physics, 59, 1225-1232.Guyodo, Y., C. Richter, and J. P. Valet (1999), Paleointensity record from Pleistocene sediments (1.4-0 Ma) off the California Margin, Journal of

Geophysical Research-Solid Earth, 104, 22953-22964.Foukal, P., C. Frohlich, H. Spruit, and T. M. L. Wigley (2006), Variations in solar luminosity and their effect on the Earth's climate, Nature, 443 ,

161-166.Frohlich, C. (2006), Solar irradiance variability since 1978 - Revision of the PMOD composite during solar cycle 21, Space Science Review,


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New research topics:

Past ocean acidification events in Earth history

and

Initiation of modern coral reef development

Atsushi SUZUKI

Geological Survey of Japan

National Institute of Advanced Industrial Science and Technology (AIST)

AIST Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8567 Japan

Ph +81-29-861-3769 Fax +81-29-861-3765 E-mail [email protected]

I have recognized two scientific themes, which can be considered as new research topics suitable

for future science plan of the Integrated Ocean Frilling Program (IODP) beyond 2012: (1) Past

ocean acidification events in Earth history, and (2) Initiation of modern (Quaternary) coral

reef development. Details of each topic are described below.

(1)Past ocean acidification events in Earth historyThe first topic involves the recently-emerged problem ocean acidification(IPCC, 2007). The

words ocean acidification could not be found in the text of the Initial Science Plan (ISP, 2001),

probably because scientific community had not yet realized the importance of this new threat to the

global ocean at the time. Since then, several researches have been conducted on the reconstruction

of paleo-pH in seawater during the glacial time and the Paleocene-Eocene thermal maximum

(PETM, 55 Ma ago). In particular, PETM event may be an analog for present-day changes due to

fossil fuel combustion and intensive studies have been conducted on the event. However, our

knowledge on the magnitude of past pH changes in the ocean is still surprisingly limited (Kleypas

et al., 2006; Figure 1).

In order to constrain the past pH changes in the ocean, systematic approach will be needed.

The boron isotope ratio of biogenic carbonate is used as a proxy for ocean pH. However, there is

concern about large uncertainties in the technique. The Zn/Ca ratio in benthic forams appears to

covary with the carbonate ion concentration of bottom waters. More calibration experiments are

needed for improving reliability of these proxies. Relationship among seawater pH, carbonate

production by marine calcifiers and community structure of marine organisms is an important topic.

There seems to be evolutionary responses of calcifiers against the long-term changes in the

carbonate chemistry in the ocean. Materials recovered by scientific drilling from marine deposits

would be suitable for better examination on the hypotheses. Within 5-6 years, the next IPCC report

will be due and published. Scientific results relating past-pH changes in the ocean will be cited by

the future version of IPCC reports for showing the range of natural variations of the Earth systems.

(2)Initiation of modern coral reef development


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The second theme is on the initiation of modern (Quaternary) coral reef development and the major

questions of the research are when and why modern coral reef development started? Scientific

drilling in the Great Barrier Reef revealed that coral reef formation was initiated ca. 600 kyr ago

(Alexander et al., 2001; Figure 2). Similar results have been reported from Ryukyu Islands in the

NW Pacific (Sakai, 2003). Hawaiis oldest drowned reef terrace located at 1440 m below sea level

was correlated to MIS15 (ca. 600 kyr ago, Webster et al., 2007). The timing of the earliest coral

atoll development on Henderson Island (Eastern Pacific) extends back to at least MIS 15

(570620 ka) (Andersen, 2008). These agreements could indicate that MIS 15 coral reef development

was synchronous across much of the Indo-Pacific region at least. This topic was not directly

discussed in the ISP, although environmental changes in the mid Pleistocene were recognized as an

important topic.

The reason for this increase in shallow water coral formation is still under debate. The onset of

larger amplitude saw-tooth 100 k.y. cycles at marine isotope stage 17 may be a trigger for the

initiation of coral reef growth (Alexander et al., 2001). Increased warming of the Pacific warm pool

(Sakai, 2003) or changes in ocean chemistry (Lawrence and Herbert, 2005) were also proposed as a

controlling factor of the initiation of coral reef developments. The supply and recruitment of coral

larvae from distant sources would be another factor for supporting reef growth (Andersen, 2008).

To test hypothesis relating coral reef initiation, deeper drilling of coral reef deposits over several

glacial cycles will be needed and may stimulate a broad range of study listed below:

1)High-resolution paleoclimate reconstruction over the several glacial cycles: Well-preserved

fossil corals provide paleoclimate information for well-dated windows of the more distant past.

By employing isotopic ( O) and trace element (Sr/Ca, Mg/Ca) technique in concert, changes in

both SST and seawater O (related to salinity and hydrological balance) can be resolved (dual

proxy technique). The method allow us to assess the seasonal and long-term variabilities of SST

and precipitation anomalies, as well as the frequency and magnitude of ENSO and

Monsoon-related events, for several glacial cycles.

2)Long-term variation in coral reef health: High water temperature destroys the symbiotic

relationship between the host coral and algae and results in coral. Suzuki et al. (2003) indicated

that isotopic microprofiling method may be the key to identifying gaps in coral growth that are

diagnostic of past bleaching events. In addition, skeletal 3C or the relationship between

3C

and 8O can be used as a potential indicator of metabolic condition of corals, or coral health

(Suzuki et al., 2003). Coral reefs have been influenced by several severe events in the past

including rapid sea-level and temperature change. Understanding of the past coral health

condition may be important to predict future change in coral reef ecosystems.

Historical changes of carbon cycle in coral reef systems would be another subtopic, which may be

related to natural variation in seawater pH during the glacial cycles.


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-3-

Figure 1. Geologic history and projection of (a) atmospheric pCO2 and (b) modeled changes in pH over the

same time period. Horizontal dashed lines indicate the range of predicted pCO2 peak atmospheric CO2

concentration over the next century. Dark lines are average historical pCO2 values, while gray shading

indicates one standard deviation. After Ridgwell and Zeebe (2005)

Figure 2. The origin of the Australian Great Barrier Reef (Alexander et al., 2001). MPR, is mid-Pleistocene

revolution in cyclicity of deep-sea foraminiferal calcite 18

O record. First 100 k.y. 18

O cycle is often

considered to be marine isotope stages 22 and 23, but classical large-amplitude saw tooth 100 k.y. cycles didnot appear until stage 17.


24/89

-4-

References

Alexander I, Andres M, Braithwaite C, Braga JC, Cooper MJ, Davies PJ, Elderfield H, Gilmour MA, Kay

RLF, Kroon D, McKenzie J, Montaggioni L, Skinner A, Thompson R, Vasconcelos C, Webster J,

Wilson P (2001) New constraints on the origin of the Australian Great Barrier Reef: results from aninternational project of deep coring. Geology 29:483486.

Andersen, M.B., Stirling, C.H., Potter, E.-K., Halliday, A.N., Blake, S. G., McCulloch, M. T., Ayling, B. F.,

O'Leary, M.(2008) High-precision U-series measurements of more than 500,000 year old fossil corals.

Earth and Planetary Science Letters, 265, 229-245.

IPCC (2007) Climate change 2007: the physical science basis. Contribution of Working Group I to the fourth

assessment report of the Intergovernmental Panel on Climate Change. Cambridge University Press,

Cambridge.

Kleypas, J.A., R.A. Feely, V.J. Fabry, C. Langdon, C.L. Sabine, and L.L. Robbins (2006) Impacts of Ocean

Acidification on Coral Reefs and Other Marine Calcifiers: A Guide for Future Research, report of a

workshop held 1820 April 2005, St. Petersburg, FL, sponsored by NSF, NOAA, and the U.S.

Geological Survey, 88 pp.

Lawrence, K.T., Herbert, T.D. (2005) Late quaternary sea-surface temperatures in the western coral sea:implications for the growth of the Australian Great Barrier Reef. Geology 33 (8), 677-680.

Ridgwell, A., Zeebeb, R.E. (2005) The role of the global carbonate cycle in the regulation and evolution of

the Earth system. Earth and Planetary Science Letters, 234, 299-315.

Sakai, S., 2003. Shallow-water carbonates record marginal to open ocean Quaternary paleoceanographic

evolution. Paleoceanography, 18 (4).

Suzuki, A., Gagan, M. K., Fabricius, K., Isdale, P. J., Yukino, I., and Kawahata, H. (2003) Skeletal isotope

microprofiles of growth perturbations in Porites corals during the 1997-1998 mass bleaching event.

Coral Reefs, 22, 357-369.

Webster, J. M., Wallace, L., Clague, D., and Braga, J. C., 2007, Numerical modeling of the growth and

drowning of Hawaiian coral reefs during the last two glacial cycles (0-250 kyr): Geoch. Geophys.

Geosyst v. 8, no. Q03011, p. doi:10.1029/2006GC001415.


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BI-POLAR TEMPERATE OCEANS AS A TEMPERATE SHOCK-ABSORBING

Noritoshi Suzuki (Tohoku Univ.) & Yoshiaki Aita (Utsunomiya Univ.)

IntroductionStrong paleoceanographic changes have been triggered by the North Atlantic and

the southern oceans, but the effect of the Pacific is little understood on the precise

resolution of view. The Pacific is so large that this ocean might be a paleoceanographic

shock-absorbing against the extreme changes in the North Atlantic and southernoceans. This shock-absorbing may be exist in the temperate regions of the both

hemisphere, because the volumes of temperate oceans are changeable with the balance

between cool and warm waters. If shock-absorbing disappears with the enhancement

of one or both waters, the global extreme paleoceanographic changes could start.

Temperate regions in the North Pacific is also a mixed region of different water masses,

which causes to produce new marine organisms with competition for survival, and to

jump the population of marine organisms in the chance of mixture.

My backgroundWe have been studying the temperate radiolarian faunal changes from the Middle

Eocene to Pliocene in the temperate North Pacific and the temperate South Pacific.

Radiolarians show zonal distribution probably with zonal sea water temperature, and

it was presumed that faunal assemblages showed similar between the both temperate

oceans. The species composition of both temperate oceans is rather comparable, but we

recognize many issues:

(1) In regardless of similar ecological regions (e.g. temperature, salinity, nutrient

in the modern oceans), the dominated species are definitely different between

them;

(2) The majority of the dominant species does not live in the tropical zones, why

can the same (morphologic) species be separately distributed in the both

hemisphere, even for the trophic species;


26/89

(3) Tropical and cool species were occasionally invaded in the temperate North

Pacific, but it has not recorded in the temperate South Pacific;

(4) Our comparisons between the temperate North and South Pacific conclude that

the similar composition of radiolarian species has established in the Early

Miocene, at least. When did the similarity start? Did the temperate species can

evolved in the same matter since the Early Miocene? Is there no possibility on

the faunal replacement?;

(5) Similar phenomena seem to be recognized in planktic foraminifers, mollusks

and others. What kind of marine organisms made such bi-polar distribution?;

and(6) The paleoceanographic system for the establishment and sustainment of the

bi-polar distribution is unknown.

Based on the knowledge of Late Eocene to Pliocene radiolarians in the temperate

North and South Pacific, temperate oceans are important target not only for

shock-absorbing but also the evolution of marine organisms.

TargetThe suitable samples are very limitedly recovered from the temperate North Pacific

and South Pacific to solve such issues, probably because of non-calcareous sediments.

However, the biostratigraphy of radiolarians and diatoms has progressed in the both

temperate region, the thoughtful study can start under the current biostratigraphic

knowledge. Target samples should be cored from siliceous sediments as well as

calcareous sediments in these regions, although the target sites should be selected

with preliminary investigation.

Stratigraphic intervals: From the uppermost Eocene to Pleistocene;

Zones: 35 to 45 paleo-latitudes in the North and South Pacific.

Target organisms: radiolarians, diatoms, dinoflagellate, nanno-fossil, and forams.


27/89

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28/89


29/89

Itsuki Suto (Nagoya Universit y, e-mail:[email protected])

Importance ofChaetoceros

resting spore studiesThe marine diatom genus Chaetoceros is one of the most important taxa in present

oceans, especially coastal upwelling regions (Hasle & Syvertsen, 1996) and their

contribution accounts for 20-25% of total marine primary production (Werner, 1977). Under

nutrient-rich conditions, most Chaetoceros species reproduce rapidly and form long chains

of thin-walled cells, just like normal vegetative diatoms, but their valves are not preserved as

fossil due to dissolution (Itakura, 2000). On the other hand, as nutrient supplies are depleted,

most of them form thick-walled resting spores which sink to the sea floor, where they await

the return of favorable conditions that nutrients are provided again by upwelling (McQuoid &

Hobson, 1996). The heavily silicified resting spore valves are preserved in sediment as

fossils and abundantly occurred from near-shore sediments in association with other fossil

diatom valves. The fossil resting spores can be preserved as significant constituents

in fossil marine diatom assemblages, which provide useful information for

reconstructing paleoproductivity and paleoenvironmental changes.

Chaetoceros Explosion Event across the Eocene/Oligocene boundary

The taxonomy of resting spores is less well understood because their corresponding

vegetative frustules are rarely preserved along with the resting spores and their valve

structures are simple. No attention, therefore, has been paid to the significance of resting

spores from a geological point of view, which contrast well with that the taxonomy and

biostratigraphy of fossil diatoms from Cenozoic sediments have been studied intensively in

several oceans by using marine sedimentary successions collected by the DSDP, ODP and

IODP (e.g. Yanagisawa & Akiba, 1998).

Recently, a firm taxonomic basis form the classification of fossil resting spores in

biostratigraphic and paleoceanographic research, using Eocene through the Recent

samples from DSDP Site 338 in the Norwegian Sea, Site 436 and Holes 438A&B in

north-western Pacific and several on-land sections (e.g. Suto, 2006). As the result, distinct

resting spore event (Chaetoceros Explosion Event, CEE), including abrupt changes

in their species richness (explosive 10-fold increasing), abundance (abruptly

increasing) and their average valve sizes (half reducing) was documented from the

DSDP Site 338 within a ~6 myr time interval across the Eocene/Oligocene boundary

(Suto, 2006). Based on evaluation of the ecologic differences between Chaetoceros and

cyst-forming dinoflagellates, Suto (2006) indicated that i) the role of main primary

producer might have switched from dinoflagellate in the Eocene to diatom, especially


30/89

Chaetoceros, in the Oligocene; ii) the conditions in the Norwegian Sea changed from

stable with a constant (annual) nutrient supply provided by upwelling in win ter in the

Eocene, to unstable with a sporadic supply of nutrients by increased vertical mixing inthe Ocean after the development of Antarctic Circumpolar Current leading enhanced

nutrient supply to the surface waters (Falkowski et al., 2004).

The CEE event was also recognized in the DSDP Holes 366 and 369A, eastern equatorial

Atlantic Ocean (Suto, in prep.), the event, therefore, might occur in all over the world oceans.

Moreover, the evolution of the Mysticeti (baleen whales), which consumes a lot of copepods

mainly eating diatoms, from the Archaeoceti (paleowhale) across the Eocene/Oligocene

boundary, coincides with CEE. Consequently, CEE is likely to have enhanced the

evolution of whales (Chaetoceros-baleen whale co-evolution hypothesis)(Suto

presented in AGU, 2007).

Proposed locations for coring

In order to testify the CEE hypothesis, we need to study core samples containing

fossils ofChaetoceros resting spores collected from the high latitude, near-shore

upwelling regions where baleen whales are feeding (e.g Southern and North Pacific

Oceans) before breeding in low latitudes.

For this study, we need samples from the continuous marine sedimentary succession with

Chaetoceros resting spores from the Eocene to the Oligocene with little gaps. But there are

limited core samples covering E/O boundary because the upper Eocene sediments have

been eroded in many marine cores and there is a hiatus at that boundary (e.g. DSDP Sites

274, 338, ODP Site 908). Moreover, the information on changes in abundance of resting

spore in association with those of normal fossil diatom valves cores is very limited.

Furthermore, it is difficult to know the occurrence of resting spores from the previously

published literatures, because they have been out of the scope of investigations for most of

diatom researchers.

If we can collect core samples from Eocene to Oligocene sedimentary successions

without any gap from the upwelling region in the Southern Ocean, we will achieved not only

to reconstruct the paleoproductivity and paleoenvironmental changes in the ocean

and to clarify the causes, process, and effect of CEE and the evolution of baleen

whale enhanced by diatoms, but also to establish and refine an Eocene through

Oligocene normal diatom zonation which will increase reliability of diatom

biostratigraphy.


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Plio-Pleistocene Evolution and Glacial/Interglacial Changes in the Bering Sea:Summary of Scientific Drilling Objectives for an IODP Expedition

Kozo Takahashi (Kyushu U), Christina Ravelo (UC Santa Cruz) and Carlos AlvarezZarikian (IODP, Texas A & M U)

Over the last 5 my, global climate has evolved from being warm with only small

Northern Hemisphere glaciers and ice sheets (~5-3 Ma) to being cold with majorNorthern Hemisphere glaciations occurring every 100 to 40 ky. The reasons for thismajor transition are unknown. Although there are data to show that the Pacificexperienced oceanographic reorganizations that were just as dramatic as those in theAtlantic, the scarcity of data in critical regions of the Pacific (the largest ocean witharguably the largest potential to influence global climate) has prevented an evaluation ofthe role of North Pacific processes in global climate evolution.

Over the last hundreds of thousands of years, glacial/interglacial and millennial scaleclimate oscillations have occurred also due to mechanisms that are unknown, althoughseveral studies from the North Pacific subtropical and mid-latitude regions indicate thatthe generation and/or transmission of climate oscillations around the globe might involve

intermediate water ventilation of the North Pacific. Drilling in the Bering Sea to recovercomprehensive records of environmental conditions during periods of time with differentclimate boundary conditions, can help answer questions about the global extent of climateoscillations mechanisms that produce them.

This expedition will obtain sedimentary sequences study the Pliocene-Pleistoceneevolution of millennial to Milankovitch scale climatic oscillations in the Bering Sea, themarginal sea connecting the Pacific and Arctic oceans. Paleoclimatic indicators will beused to generate complete and detailed records of changes in the biological, chemical and

physical oceanographic conditions in the Bering Sea, as well as of the adjacentcontinental climate. In addition to being sensitive to regional and potentially globalclimate change, the Bering Sea is one of the source regions of the North PacificIntermediate Water (NPIW). Since the production of the NPIW is thought to be tied toglobal climate change and to Pacific Ocean circulation and nutrient distributions,investigating the evolution of conditions in regions of NPIW formation is criticalforunderstanding Pacific paleoceanography (Fig. 1).

Drilling in the Bering Sea will also document the effect of changes in the Bering StraitGateway region (Fig. 1). The Bering Strait is the main gateway through whichcommunication (flux of heat, salt and nutrients) between the Atlantic and Pacific, via theArctic Ocean, occurs today. Investigating the evolution of the Bering Strait is critical toan understanding of transitions in global ocean heat and nutrient budgets.

Detailed high resolution paleoenvironmental reconstructions from the Bering Sea hasnot been achieved in the past, although there was some reconnaissance work during

DSDP Leg 19 and piston core work focused on generating paleoceanographic recordsfrom the latest Pleistocene (Fig, 2). The planned drilling, including triple APC holes at allsites, will provide the first continuous sedimentary records that can be used to reconstructthe history of this important marginal sea and its role in global changes over the past 5my.

Specifically, the sedimentary records from the Bering Sea will provide anunderstanding of:

The evolution of Pliocene-Pleistocene surface water conditions, paleoproductivity, andsea-ice coverage, including millennial to Milankovitch scale oscillations.

The history of past production of the Pacific Intermediate and/or deep water masseswithin the marginal sea, and its link to surface water processes.


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The interactions between marginal sea conditions and continental climate.

The linkages between processes in the marginal sea (e.g. variations in deep waterformation, or water mass exchange through gateways) and changes in the pelagic Pacific.

An evaluation of how the history of ocean/climate of the Bering Strait gateway region

may have had an effect on north Pacific and global conditions.

All of these scientific objectives will focus both on the long term ocean and climate trends,as well as the evolution of higher frequency glacial-interglacial to millennial scaleoscillations through the Plio-Pleistocene.

Fig. 1. Planned IODP drill sitesand highlights of the objectivesin the Bering Sea.

Fig. 2. Relative abundances ofCycladophora davisiana duringthe last 100 k.y. in the Bering Sea,the western subarctic Pacific(circle = Cores BOW-9A,BOW-12A, UMK-3A, andGAT-3A and Site ES [EmperorSeamount, in the subarcticPacific]), and the Okhotsk Sea(square = Cores PC1, PC2, andPC4; data from Okazaki et al.,2003). B. Distribution patterns ofCycladophora davisiana: the

present (redrawn from Lombari

and Boden, 1985), marine isotopestage (MIS) 1, the Last GlacialMaximum (LGM), and MIS 5-3.Arrows indicate source regions of

past NPIW (Tanaka andTakahashi, 200


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Gas hydrate in the continental margin

Hitoshi Tomaru

New Energy Resources Research Center, Kitami Institute of Technology,

Koen-cho 165, Kitami 090-8507, Hokkaido, Japan

E-mail: [email protected]

Tel: 0157-26-9533

Tectonic and climate processes, that are ones of the key topics of recent earth

sciences, constrain significantly the stability of marine gas hydrate. There have been

closely related two major aspects resulting from massive dissociation of gas hydrates in

the continental margins; seafloor instability causing a slope failure, and massive release

of methane into the marine/atmosphere environments.

Marine gas hydrates generally fill pore spaces and impart mechanical strength

of host sediments. Slight change in pressure and/or temperature of seafloor can rapidly

and widely dissociate gas hydrates because of their sensitivity to the stability condition

of pressure and temperature. The decomposition of gas hydrate-cemented sediment

releases hydrocarbon gases, mostly methane in natural environment, to the ocean and

atmosphere, which may reduce the slope stability and result in slope failure, slumping,

and landslide (Bnz et al., 2003). Furthermore, methane has a strong potential of global

warming about 20 times larger than the same volume of carbon dioxide. The global

warming caused by gas hydrate dissociation can increase global temperature and thus

induce further gas hydrate dissociation, triggering catastrophic chain reactions (Kennett

et al., 2002).

Release of huge amount of methane is also hazardous to the global system.

Seawater and possibly atmosphere become anoxic after a massive dissociation of gas

hydrates because of increased amount of methane that is strongly reductive carbon, and

may cause mass extinction. Recent studies have revealed that there are some lines of

evidence of catastrophic climate changes due to the gas hydrate dissociations.

Matsumoto (1995) and Dickens et al. (1995) pointed out the methane release from gas

hydrate during the latest Paleocene thermal maximum (LPTM) by 13C anomalies in

carbonates. A 1.121018 g of methane releasing due to hydrate dissociation with 13C of

-60 over 104 years is well consistent with the geological records (Dickens et al.,

1997). Hesselbo et al. (2000) also considered the possibility of methane hydrate


34/89

dissociation during a Jurassic anoxic event on the basis of13C anomalies in carbonates.

Kennett et al. (2000) discussed the methane release due to hydrate dissociation during

Quaternary interstadials using planktonic

18

O and

13

C anomalies in the Santa BarbaraBasin, and concluded that gas hydrate stability was modulated by intermediate-water

temperature changes induced by switches in thermocline circulation. Bratton (1999)

examined clathrate eustasy that is a mechanism of gas hydrates controlling sea level.

Sea level rise associated with thermal expansion can be offset by a decrease of hydrate

volume due to their dissociation, and this may explain anomalous sea level falls during

ice-free periods such as the early Eocene, the Cretaceous, and the Devonian.

An important issue of the research focused on marine gas hydrate system is that

these events can take place near future in relatively short time compared to other

geological events because of the strong instability of gas hydrates against the pressure

and temperature. The drilling research is useful to observe present condition of

sub-seafloor gas hydrates, observation/monitoring of the gas hydrate and the

related-phenomena, however, must be conducted to investigate and expect behavior of

gas hydrate system. Here we propose the development of observation system on gas

hydrates, e.g. monitoring of geochemical and geophysical changes of pore water, gas,

and sediment in borehole as well as the P-T conditions. Fluid and gas expulsion from

the seafloor is also an important proxy of sub-seafloor gas hydrates and is a direct input

of methane and fresh water into marine/atmospheric environments. Monitoring of the

flux and geochemistry of fluid and gas from the seafloor should be carried out together

with the deep observations to investigate the entire nature of marine gas hydrate system

and assess the potential geohazards such as landslides and global environment changes.

This research integrates the environmental change models induced by gas hydrate

dissociation in the past with that may occur in the future.

Western margin of the Pacific Ocean, including Nankai Trough, Japan Sea,

South China Sea, Okhotsk Sea, and Bering Sea, is proposed for this integrated gas

hydrate studies because of the ubiquitous presence of gas hydrates and gas

hydrate-related phenomena, e.g. gas seepage on the seafloor, and BSR and gas charged

sediment structure on seismic records, in different geological settings (Fig. 1). Both

pore space-filling and massive/nodular gas hydrates occur in backarc and forearc

locations where subduction-induced geological activities such as accretion, thrust/fault,

and earthquakes have been developed. The spacious investigation in this region is,

therefore, feasible for the comparison of factors controlling gas hydrate behavior among

occurrences, geological settings, and geological activities through the earths history.


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Reference

Bratton, J.F., 1999. Clathrate eustacy: Methane hydrate melting as a mechanism for

geologically rapid sea-level fall. Geology, 27: 915-918.Bunz, S., Mienert, J. and Berndt, C., 2003. Geological controls on the Storegga

gas-hydrate system of the mid-Norwegian continental margin. Earth Planet. Sci.

Lett., 209: 291-307.

Dickens, G.R., O'Neil, J.R., Rea, D.K. and Owen, R.M., 1995. Dissociation of oceanic

methane hydrate as a cause of the carbon isotope excursion at the end of the

Paleocene. Paleoceanography, 10: 965-971.

Dickens, G.R., Castillo, M.M. and Walker, J.C.G., 1997. A blast of gas in the latest

Paleocene: Simulating first-order effect of massive dissociation of oceanic

methane hydrate. Geology, 25: 259-262.

Hesselbo, S.P. et al., 2000. Massive dissociation of gas hydrate during a Jurassic oceanic

anoxic event. Nature, 406: 392-395.

Kennett, J.P., Cannariato, K.G., Hendy, I.L. and Behl, R.J., 2000. Carbon isotopic

evidence for methane hydrate instability during Quaternary interstadials. Science,

288: 128-133.

Kennett, J.P., Cannariato, K.G., Hendy, I.L. and Behl, R.J., 2002. Methane Hydrates in

Quaternary Climate Change: The Clathrate Gun Hypothesis. Amer Geophysical

Union, Washington, DC, 216 pp.

Matsumoto, R., 1995. Causes of the 13C anomalies of carbonates and a new paradigm

'Gas Hydrate Hypothesis'. J. Geol. Soc. Japan, 101: 902-924.


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Fig. 1: Western margin of the Pacific Ocean. Stars represent locations where gas

hydrates were collected or gas hydrate-related phenomena were observed.


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Piling-up event maps: para-para comic strategy for elucidating dynamism of global eventsduring greenhouse period

Hasegawa, Takashi (Kanazawa Univ., School of Natural Systems)

Recent progress of carbon isotope stratigraphy for important global events including

Cretaceous oceanic anoxic events (OAEs) and Paleogene thermal maximum events enable us an

orbital scale correlation between remote regions for each event. Causal factor, variation and

pattern of 4-dimentional (temporal and spatial) propagation of certain paleoceanographic event

can be discussed under age control of ~10 kyr accuracy. Here I propose global array of

paleoceanographic data for important events that allows global paleogeographic reconstruction on

each time slice at an interval of ~10 kyr. In other words, it means drawing event map that shows

paleogeographic extent of the event (extraordinary conditions) for each ~10 kyr across the eventinterval. Paleocene-Eocene thermal maximum encompassing 110 kyr requires pile-up of eleven

global event maps, for example. As is movie cartoon that is composed of silent pictures but

produces dynamic action of a hero, time series of such event map should reconstruct a dynamic

feature of each paleoceanographic/ paleoclimatological event. Here I call this strategy as

para-para comic strategy for elucidating dynamic reconstruction of greenhouse events. The

name is taken from Japanese moving line-drawing sometimes found at a corner of a comic

booklet.

Focusing on specific horizons and assembling data from various localities over the

extensive area is, however; not conformable to current operation policy of IODP vessels. While

each voyage may require less than one month as it targets specific time interval only, Para-para

comic strategy requires multiple cruise. Once the strategy appears on new science plan of next

IODP, an umbrella proposal focusing on specific event, OAE2 for example, with multiple compact

regular proposals (to drill one or two sites for each) will be submitted as a new proposal style.

The key issues of this strategy are global array of data and super high resolution. For

global array of data for greenhouse events during Cretaceous or Paleogene, extensive virgin area

remains over middle to high latitude Pacific. The difficulty for that area is derived mainly from

following reasons: Sediments on oceanic plate have been lost during the subduction. Even they

survive on the plate, they are composed of siliceous material barren in sophisticated

paleoceanographic proxy.

What contributes toward overcoming these difficulties? Two options seem to be available

for usExploring fore-arc basin sediments that preserve target events with well-preserved

carbonate microfossils is the one of them. Because the Pacific is surrounded by subduction zones,

fore-arc basins sequences are known from land as well as submarine record (the Yezo Group and

its submarine counterpart are the example. Similar sediments are known from California-British

Colombia and New Zealand). They potentially preserve useful paleo-proxy as known from theHaboro area in Hokkaido (Moriya et al., 2003). Another option is to develop paleoceanographic


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proxies for siliceous sediments. It contains very important science that contributes

paleoceanography but is beyond the scope of IODP science plan.

Once we recognize a fore-arc sedimentary sequence as a suitable target (it should

preserve continuous event sequence and carbonate material available for paleoceanographic

proxies) for certain event, we can take advantage of its sedimentation rate for super highresolution study. The rate sometimes reaches 400 m/myr (Hasegawa and Saito, 1993) and allows

us 500 yr resolution taking bioturbation into account. Fore-arc basin sediment does not preserve

only oceanic environment but also terrestrial climatic information that offers land-ocean linkage

during the event. Terrestrial information will be a crucial part of our global array of data.

Fore-arc basin drilling seems to be essential for the Para-para comic strategy.

To test the efficacy of studies on fore-arc sediments, I propose to drill off-Miyagi sequence

targeting Late Turonian Events. Based on the current knowledge about Cretaceous fore-arc basin

sediments along the NE Honshu Island (Ando, 2003), sediments of off-Miyagi Prefecturepreserves Cenomanian through early Coniacian sequence and available for studies on the proxies.

The Late Turonian sequence should record initial gradual cooling after the Cenomanian-Turonian

thermal maximum (Jenkyns et al., 1994) that can be interpreted as a first step of climatic trend

from greenhouse environment toward icehouse earth (long term aspect). A large magnitude of

eustatic sea level drop (as much as 100 m)(hardenbol et al., 1998) is remarkable short term event

during Late Turonian. The cores from off-Miyagi provide a good opportunity to evaluate

terrestrial climatic response to large scale sea level drop on the ice-free earth. Short-term carbon

isotope events (three conspicuous events, namely Bridgewick, Hitch Wood and Navigation

Events within ~500 kyr)(Jarvis et al., 2006) provide clear chemostratigraphic anchor horizons

that are prerequisite for reliable interregional correlation. From Norfolk section in the UK,

additional seven positive peaks are observed in addition to the three major carbon isotope events

suggesting potential orbital scale resolution through the Late Turonian Event interval (Jarvis et

al., 2006). Exploring OAE2 sequence associated with diagenetically not altered carbonate

microfossils for the proxy study is another important purpose of the drilling mission. Para-para

comic strategy should work effectively on resolving secular variation of the global feature through

the event.

References

Ando, H. (2003) Stratigraphic correlation of Upper Cretaceous to Paleocene forearc basin sediments in Northeast Japan: Cyclicsedimentation and basin evolution. Journal of Asian Earth Sciences, 21, 921-935.

hardenbol, J., Thierry, J., Farley, M.B., T. Jacquin, de Graciansky, P.C. and Vail, P.R. (Editors), 1998. Mesozoic and Cenozoicsequence chronostratigraphic framework of European basins. Mesozoic and Cenozoic sequence stratigraphy ofEuropean basins, 60. SEPM (Society of Sedimentary Geology) Special Publication.

Hasegawa, T. and Saito, T. (1993) Global synchroneity of a positive carbon isotope excursion at the Cenomanian/Turonianboundary: validation by calcareous microfossil biostratigraphy of the Yezo Group, Hokkaido, Japan. Island Arc, 2,181-191.

Jarvis, I., Gale, A.S., Jenkyns, H.C. and Pearce, M.A. (2006) Secular variation in Late Cretaceous carbon isotopes: A new 13Ccarbonate reference curve for the Cenomanian-Campanian (99.6-70.6 Ma). Geological Magazine, 143, 561-608.

Jenkyns, H.C., Gale, A.S. and Corfield, R.M. (1994) Carbon- and oxygen-isotope stratigraphy of the English Chalk and ItalianScaglia and its palaeoclimatic significance. Geological Magazine, 131, 1-34.

Moriya, K., Tanabe, K., Nishi, H., Kawahata, H. and Takayanagi, Y. (2003) Demersal habitat of Late Cretaceous ammonoids:Evidence from oxygen isotopes for the campaign (Late Cretaceous) northwestern Pacific thermal structure. Geology, 31,167-170.


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Reconstruction of the atmospheric circulation system during the past greenhouse

period

Hitoshi Hasegawa, Ryuji Tada (The University of Tokyo)

Understanding the behaviour of the Earths climate system during the past greenhouse

period has profound implications for the consequences of ongoing global warming. Proxy data

demonstrated that the equator-to-pole temperature gradient was much lower during the

mid-Cretaceous and/or early Eocene supergreenhouse periods than at present, implying larger

meridional heat transport by intensified atmospheric and/or oceanic circulation. However,

reconstruction of atmospheric circulation during the Cretaceous has been hampered by a lack of

appropriate data sets based on reliable proxies. We reconstructed temporal changes in the latitude

of the subtropical high-pressure belt and its divergence axis during the Cretaceous, based on a

reconstruction of spatio-temporal changes in the latitudinal distribution of desert deposits and the

prevailing surface-wind patterns recorded in the Asian interior (Fig. 1). We found a poleward

shift in the subtropical high-pressure belt during the early and late Cretaceous greenhouse

periods, suggesting a poleward expansion of the Hadley circulation. In contrast, an equatorward

shift of the belt was found during the mid-Cretaceous extremely warm supergreenhouse period,

suggesting drastic shrinking of the Hadley circulation (Fig. 2). These results, in conjunction with

recent observations of increasing Hadley cell width with the increase in atmospheric CO2 level,

suggest the existence of a threshold in atmospheric pCO2 and/or global temperature, beyond

which the Hadley circulation shrinks drastically (Fig. 3).

In search for supporting evidences of such drastic shrinking of the Hadley circulation

during the past greenhouse period, reconstruction of the paleo-location of the subtropical

high-pressure belt from the marine record is essential. Therefore, we propose to conduct

latitudinal transects of pelagic sea sediment cores of the mid-Cretaceous and/or PETM and early

Eocene ages from the central Pacific and/or central Atlantic. Eolian records (grain-size, flux,

lithologic composition) in pelagic sea sediment might provide us with information on the

changes in latitudinal distributions of the subtropical high-pressure belt at that time.


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Fig. 1 Spatio-temporal changes

in the distribution of climate-

sensitive sediments and paleo-

wind directions in the Asianinterior during the Cretaceous.

Fig. 2 Temporal changes in the

latitude of the subtropical high-

pressure belt, calculated sea surface

temperatures (SSTs), and occurrences

of ocean anoxic events (OAEs)

during the Cretaceous.

Fig. 3 Inferred evolutionary trends of

the changing atmospheric circulation

pattern in response to climatic

warming (from icehouse to

greenhouse), and the conceptual

scheme of the latitudinal changes in

the width of the Hadley circulation vs.

atmospheric CO2 levels.


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IODP Research proposals

Kazuhiko Fujita (University of the Ryukyus)

1. Revealing causes, timing and magnitudes of sea-level changes during Terminations

During glacial-interglacial transitions known as Terminations, ice volume decreased,

instead sea level, temperatures, and greenhouse gas concentrations increased abruptly (e.g.,

Petit et al., 1999 in Nature; Lambeck et al., 2002 in Nature). Thus, Terminations are regarded

as possible analogues for modern climate changes and associated rapid environmental changes.

Since key parameters such as ice volume, sea level and temperature are closely related to each

other, the precise reconstruction of sea levels during Terminations is critical for understanding

ice-sheet dynamics and suborbital climate variability. Previous studies showed that the last

deglaciation (Termination I: TI) was characterized by rising sea levels and SSTs associated

with several rapid climate events such as meltwater pulses (MWPs) and Younger Dryas (YD)

climate reversal. Detailed climate and environmental changes during TI will be revealed soon

by IODP Expedition 310 (Tahiti Sea-Level) and the forthcoming Great Barrier Reef

Expedition.

On the other hand, structures of older Terminations are not yet clear. Particularly,

course, timing, and magnitude of sea-level changes during older Terminations have yet to be

reconstructed in detail. Studies on the termination of the penultimate glacial period

(Termination II: TII) are progressing and revealing the timing, events and suborbital variability

of climate changes during this deglaciation (e.g., Cannariato and Kennett, 2005 in Geology;

Siddall et al., 2006 in Geology). Lately, a new shallow-water sequence has been found from

offshore Tahiti by IODP Exp. 310 (Fujita et al., submitted; Iryu et al., submitted), which is the

first complete and direct evidence to record sea levels and associated environmental changes

during TII. The sea-level changes during TII reconstructed by these works were characterized

by the two steps of rising sea-levels with intervening sea-level drop, suggesting the presence of

the sea-level reversal event during TII (Esat et al., 1999 in Science; Siddall et al., 2006 in

Geology). Such sea-level reversal event is similar to the YD climate reversal event, though the

YD event was not associated with sea-level drop. However, there remains to be answered if

this phenomenon was common during the periods of rising sea levels or unusual only during

TII. Furthermore, causes of the sea-level reversal events during TII and older Terminations if

exists are not yet known.

Thus, the purposes of this proposal are 1) to reconstruct sea levels and associated

environmental changes during older Terminations, 2) to compare similarity and differences in

sea-level changes among several Terminations, and 3) to reveal the existence and causes of

sea-level reversal events during Terminations. Resulting sea-level data and associated


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environmental records will contribute to 1) the modeling of ice-sheet dynamics and 2) the

understanding of biological responses such as coral reefs to rapid environmental changes.

Proposed drilling sites are French Polynesia (Tahiti), which has tectonically slow and

constant subsidence rates and is located at considerable distance from the former major ice

sheets (far-field). Several cores on transects from shallow shelf to shelf slope are recovered and

analyzed. Collaboration with carbonate sedimentologists (sequence stratigraphy),

paleontologists (paleodepth estimates by reef fossils), and geochemists (u-series dating by

corals, SST/SSS by coral archives) are required.

2. Interactions between secular variations in seawater chemistry and bio-calcifications

Biomineralization of marine organisms is controlled not only by intrinsic factors(cellular activity), but also by external (environmental) factors such as seawater chemistry.

Recent studies revealed that the magnesium/calcium (Mg/Ca) ratio and absolute

concentration of Ca in seawater have oscillated during Phanerozoic time, which has

been driven by changes in rates of deep-sea igneous activity. Such secular variations in

seawater chemistry influenced the precipitation of non-skeletal carbonates (e.g.,

Hardie, 1996 in Geology). Experimental and paleontological evid

atmosphericco2glaciationoceanbiogeochemcenozoic--ahagon

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