orbital forcings the ocean-atmosphere system: primary responses to orbital forcings atmosphere ocean...

Orbital forcings

The ocean-atmosphere system:primary responses to orbital

forcings

ATMOSPHERE

OCEAN

temperaturehumidity

CO2winds

GLACIAL

volumetemperature

CO2currents

INTERGLACIAL

The oceanic d18O record:

80-90% RSL response;10-20%

temperatureresponse?

SST changes

from LGM to present in coastal

waters of N. California

(~100 km offshore?)

Radiolarian assemblages in core 1019 (989 m water depth)

green line = GISP2 18O record; black line=radiolarian record

T1YD

Primary productivity and zones of coastal upwelling

image: terra.nasa.gov

Pelagic diatom assemblages of the N. Pacific

(e.g. Okhotsk Sea cluster = one of three subarctic water masses, shown in black)

from: Sancetta & Silvestri (1986) Paleoceanography 1, 163-180.

579

580

V20-119

V20-107

V21-172RC10-216

“Okhotsk

cluster” through

time

RSL -temperature - salinity interactions in the Red Sea

Low RSL = hypersaline Red Sea = no planktonic forams

from

: R

ohlin

g e

t al. (

1998)

Natu

re,

394,

162-1

65.

A Heinrich

layer (H-1) in a

deep-sea core

pela

gic

ooze

ooze

H -

layer

(ooze

-fille

d b

urr

ow

s?)

Iceberg-rafted detritus (IRD) in H1

Heinrich events in the North Atlantic Ocean

Oceanographic effects of drifting icebergs

>200 m

drift

cold fresh water

nutrient-deficient

nutrient-rich detritus

Heinrich (5-10 ka) events

and Bond cycles

(~1.5 ka)in VM23-

81

N.

Atl

anti

c cu

rrents

:ic

eberg

-dri

ft r

oute

s

The N. Atlantic ‘gate’ and the ‘binge-purge’ cycle of the Laurentide ice

sheet

Ocean‘polar front’

cold

warm

Dansgaard-Oeschger cycles and Heinrich events

Thermohaline circulation

Binge and purge: is there a Heinrich record in Antarctica?

antiphasing?

Inferred Late

Glacial and

Holocene SST

(Aegean Sea)

from: Geraga et al., (2000), Palaeo3, 156, 1-17

YD

H1

SST C(org)%

Sapropel stratum in a core from the eastern

Mediterranean

(“sapro” = putrid - refers to high Corg content); “pel” = mud

Episodes of sapropel

formation in the last 200 000

years in the eastern

Mediterranean

from: Kallel et al., (2000), Palaeo3, 157, 45-58

S1 S3 S4 S5 S6 S7

30°N

Laminated sapropel deposits

from: Kemp et al., (1999), Nature, 398, 57-61

Sapropels:annually

laminated diatom mats

from: Kemp et al., (1999), Nature, 398, 57-61

Sapropel formation hypothesisafter Kemp et al., (1999), Nature, 398, 57-61.

(see Sancetta (1999), Nature 398, 27-29 for discussion)

• Greater freshwater runoff to eastern Mediterranean (heavy rainfall in Nile headwaters and in Med. Basin); leads to:• Enhanced stratification of surface waters, produces ‘nutricline’ across surface halocline; leads to:• Massive bloom of diatoms adapted to stratified waters (chiefly Rhizosolenia spp. and Hemiaulus hauckii).• Winter mixing of water column causes mass sinking of diatom mats.• Mixing brings nutrients to surface, promoting conventional near- surface winter blooms of mixed diatoms.

Freshwater sources in the Mediterranean

base map from: Kallel et al., (2000), Palaeo3, 157, 45-58

Sapropels and climate of the Nile basin

S1a S1b

“sapropelic”Eastern Mediterranean sedimentary record*

Eastern Saharan sedimentary and archaeological record**

* Geraga et al., (2000), Palaeo3, 156, 1-17** Malville et al., (1998), Nature 392, 488-491

arid wet arid

11 10 9 8 7 6 5 4 3 2 1 0 ka BP

Location of core74 KL in

the Arabian

Sea

74 KL: 18O, dust deposition and CaCo3

production

Dust minimum

78508850

Sahara dust storm over adjacent Atlantic Ocean

image: terra.nasa.gov

Dust accumulation and palaeoproductivity (core Meteor 12392: on continental rise offshore of Spanish

Sahara)

Japan Sea dust record

Dust source: Mongolia/N. China

Iron fertilization experiment:polar Southern Ocean (I)

days

from

: B

oyd e

t al., (2

00

0),

N

atu

re 4

07

, 6

95

-70

2.

Iron fertilization experiment:polar Southern Ocean (II)

Mechanisms of CO2 drawdown

CO2 drawdown (Vostok)

Iron fertilization experiment:polar Southern Ocean (III)

DMS makes clouds “brighter than white”

from: Charlson et al., (1987) Nature 326, 655-661

Points to considerOcean/atmosphere temperature - CO2 - sea

icefeedbacks.

Continental climates and oceanic responses:dust exports and palaeoproductivity;monsoonal rains and sapropels;glacial surging and THC switching.

Palaeoproductivity patterns: consider effects of currents, RSL and marine food chains.