Profile of David M. Karl

From the moment 17-year-old DavidKarl first glimpsed the ocean fromthe summit of Cadillac Mountainon Maine’s Mount Desert Island,

he was captivated by the blue waters sur-rounding the fog-veiled islands. Sincethen, he has contributed to some of theworld’s most pivotal discoveries in ocean-ography. Karl, who was elected to theNational Academy of Sciences (NAS) in2006 and is now a professor of oceanog-raphy at the School of Ocean and EarthScience and Technology at the Universityof Hawaii, has witnessed iconic momentslike the discovery of hydrothermal vents atthe Galapagos Rift. His work on 23 re-search expeditions to Antarctica helped toreveal the unanticipated thriving foodweb that exists in those frigid waters. Hehas developed or refined more than 50analytical methods to probe ocean lifeand biogeochemistry. Many, like theMAGnesium Induced Co-precipitation(MAGIC) method for measuring phos-phate, have been widely adopted. Thework that has earned him the most rec-ognition, however, is the Hawaii OceanTime-series (HOT) program.Since 1988, HOT program researchers

have made monthly measurements ofwater column biogeochemistry and mi-crobial dynamics at Station ALOHA, a site∼100 km north of Oahu. Their datasetsare freely available and have been usedby hundreds of researchers worldwide.Themost startlingfinding to emerge from

HOTprogramdata is that climate change isaffecting the ocean ecosystem. Data fromthe HOT program provided the first “bul-letproof” evidence that rising atmosphericcarbon dioxide (CO2) from burning fossilfuels is making the ocean more acidic,a finding that was published in PNAS andwon the 2009 Cozzarelli Prize (1).Karl’s work has garnered many honors,

including the G. Evelyn Hutchinson Medalfrom the American Society for Limnologyand Oceanography in 1998, the A. G.Huntsman Medal from the Bedford In-stitute of Oceanography in 2001, theHenry Bryant Bigelow Medal in Ocean-ography from the Woods Hole Oceano-graphic Institution in 2004, and the DavidPackard Medal in Oceanography fromthe Monterey Bay Aquarium ResearchInstitute in 2005. Karl has received fel-lowships in the American GeophysicalUnion and the American Academy ofMicrobiology, and he received an honor-ary Doctor of Science degree from Uni-versity of Chicago in 2010. Now, at theUniversity of Hawaii, he directs the Centerfor Microbial Oceanography: Researchand Education (C-MORE), a National

Science Foundation (NSF) Science andTechnology Center.

Call of the SeaDavid Karl, born May 9, 1950, in Buffalo,New York, was an unlikely candidatefor future NAS membership. Althoughhe ranked in the top 5% of his class inschool, he did not enjoy learning. “I wasthe dunce of the academically talented;I spent most of my time outdoors playingsports, mostly baseball.” Looking back,Karl says that his involvement in sportswas a “life lesson in discipline andteam spirit.”Karl’s team-building skills would later

serve him well in science. Although helacked passion for schoolwork, he wasinterested in people and leadership, andhe served as class president for his last3 years of high school (1965–1968), a tu-multuous era that he says was “an excitingtime to be in student government.”If he was trying to avoid an academic

career, however, the oddswere against him.His brother and sister were National MeritScholars, and although his parents were notcollege-educated—his father was a self-employed soft drink distributor and, later,amailman,andhismotherwas a librarian—they expected him to go to college.Early on, Karl wanted to be a com-

mercial fisherman, a desire sparked bywatching documentaries on tuna fishingand strengthened by summer fishing tripson New York’s Finger Lakes. Readingpiqued his interest in the ocean, however.

His mother knew that reading was theticket to a good education and broughthome books about fish anatomy, fisheriesscience, and even Arthur C. Clarke’sThe Challenges of the Sea (2). “She wastrying to get me to set a target a little bithigher than becoming a commercial fish-erman,” Karl recalls.Karl’s parents gave their children a

long leash, encouraging their interest inthe hippie movement; Karl’s father evenhelped him pick out a motorcycle whenDavid was 15 years old. They also fi-nanced his trek to the 1969 Festival ofMusic and Art, also known as Woodstock.“It was all about direction without guid-ance but with plenty of love,” he says.

Florida, Not FishAfter the 17-year-old’s fateful trip to thesummit of Maine’s Cadillac Mountain,Karl decided to study biology at the StateUniversity College of New York at Buf-falo. He graduated in 3½ years, magnacum laude. Frustrated with teaching“book classes” like algebra and physicalscience at an inner-city vocational highschool, Karl applied to graduate ocean-ography programs and was eventuallyaccepted at Florida State University, aprogram that boasted a seagoing vesseland distinguished faculty.He intended to study coral reef fishes;

however, his advisor, Paul LaRock, stud-ied ocean-dwelling microorganisms andconvinced Karl to do the same. LaRockwas such a good mentor and teacher thatKarl “just fell in love with the subjectmatter.” LaRock stepped beyond aca-demics, exposing him to contemporaryresearch problems and introducing him toother scientists.Two years later, MS degree in hand,

Karl attended Holger Jannasch’s summercourse on microbial ecology at the Ma-rine Biological Laboratory in WoodsHole, Massachusetts. During the summerof 1974, after several rejected applica-tions in years past, Karl was admitted toa PhD program at The Scripps Institutionof Oceanography (SIO) in La Jolla, Cal-ifornia. He spent the next 3½ years in thelaboratory, in the library, and aboard re-search vessels at sea. His PhD projectearned him the prestigious Eckard Prizein 1979 for best dissertation of the year.

Exotic CruisesSoon after Karl arrived at SIO, Jannaschinvited him to participate in a month-long

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David M. Karl.

This is a Profile of a recently elected member of the Na-tional Academy of Sciences to accompany the member’sInaugural Article on page 1842.

www.pnas.org/cgi/doi/10.1073/pnas.1103075108 PNAS | February 7, 2012 | vol. 109 | no. 6 | 1811–1813

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expedition to the Black Sea, a poorlystudied area that had been off limits toAmerican ships for more than 10 yearsbecause of the Cold War. Scientists con-sider the Black Sea an extreme environ-ment: below 50 m, the oxygen dissipates,and between 200 and 2,500 m, there isnone. This expedition provided a peekinto a world of “relic communities” thatmay have existed before the emergence ofan oxygen-rich world more than 2 billionyears ago. Karl analyzed the distributionof microbial life there using methodshe had developed at Florida State Uni-versity (3).In 1976, Osmund Holm-Hansen, Karl’s

coadvisor at SIO, received funding for abold research program to drill throughthe ∼400-m-thick Ross Ice Shelf in Ant-arctica and sample the dark ocean be-neath it. Just hours before they were setto depart from New Zealand to Antarc-tica, equipment failure postponed theproject for a year. Karl and a colleaguewent anyway, however, for the sheer ad-venture and to do whatever contingencyscience they could muster.They traveled from McMurdo Sound to

the Dry Valley Lakes and to South PoleStation, flying between points in VietnamWar-era helicopters and ski-equippedLC-130 Hercules cargo planes.Since then, Karl has returned to Ant-

arctica on 22 more expeditions, many ofwhich were made on behalf of the Re-search on Antarctic Coastal EcosystemRates (RACER) and Palmer Long-TermEcological Research (LTER) programs.Karl and his fellow RACER and LTERprogram researchers conducted the first“time-series” experiments (4) in a body ofwater south of 60 °S latitude that hadbeen studied for many years but did nothave a formal designation until the USGeographical Board of Names approvedKarl’s proposal to dub it the “SouthernOcean” in 1999. Later that year, Karlpublished the first account of microorgan-isms in the accreted ice of Lake Vostok,an ancient subglacial lake in easternAntarctica (5).

How Many, How Much?During the early years of Karl’s career,there was little quantitative understandingof the role that microorganisms played inthe sea—how many there were and whatthey did. “We didn’t know the very basicsof the marine food web,”Karl remembers.Application of fluorescent microscopy re-vealed there were a thousand times morebacteria in a drop of seawater than werepresent by traditional plate count; whichmethod was more accurate?In the late 1960s, Holm-Hansen de-

veloped a new way of quantifying oceanmicrobes—by measuring ATP, the com-mon energy currency of life. LaRock and

Karl improved the assay at Florida StateUniversity and first applied it to marinesediments (6). “I learned early on in mycareer that if you develop a new assay orif you borrow and adapt an assay fromsome other field of study, it opens a newwindow of opportunity,” says Karl.Using this assay, Karl and his colleagues

established the distribution and abun-dance of microbial life in many regions ofthe global ocean, a delicate balance thatarises from production of new biomassfrom nutrient and energy supply and celllosses resulting from grazing, viral lysis,and death (7). Even today these processesare contemporary research topics in mi-crobial oceanography, the discipline hehelped to create during the past decade (8).

Fairyland of Exotic ColorsJust before completing his PhD degree in1977, Karl was offered a faculty position atthe University of Hawaii. The year before,Bob Ballard, John Corliss, and others haddiscovered communities of giant whitetubeworms living around hydrothermalvents in the deep sea of the GalapagosRift. Jannasch and Karl collaborated onan NSF proposal to test the hypothesisthat microbes in the Galapagos Rift mightharness energy from the sulfur bubblingup from the molten earth, much like themicrobes in the Black Sea. With Karl’sfirst NSF grant under his belt, he headedfor the Galapagos Rift hydrothermalvents to study the newest form of life onthe planet.On a return expedition in 1979, Ballard

could not find the vents on the firstdive, but Karl and fellow researcherJames Childress from the University ofCalifornia, Santa Barbara, landed right onthem on the second dive. It took more

than 1½ hours for the submarine to sink.“All you see is bioluminescence in thedeep sea, and then suddenly you hit thebottom and there’s this fairyland of exoticorganisms and all the colors. . . iron-stained basalts, bright yellow sulfur, andblood red Riftia plumes, to name a few. Itwas just incredible. We were literally thefirst biologists to see the deep-sea hydro-thermal vents. This became one of themost important discoveries in the past100 years in oceanography and revealedhow little we actually knew about ourplanet,” Karl says.Karl and Jannasch showed that micro-

organisms consumed chemicals spewingfrom the vents, forming the base of thedeep-sea food chain. They published theseminal scientific paper on the nature ofthe food web at these hydrothermal sys-tems (9). “That was a good start to myacademic career,” says Karl.He continued these investigations at

hydrothermal vents located at 11 °N and21 °N on the East Pacific Rise and in theGuaymas Basin. Ten years later, he dis-covered another hydrothermal systemnear Hawaii around the emerging islandof Loihi (10).

Hot Vents to HOT ProgramKarl studied hydrothermal vents for morethan a decade and edited a book capturingthe scientific results to date (11). Even-tually, he turned his focus elsewhere, re-alizing studies of the hydrothermal ventsystem would require deep-sea observa-tories and 50–100 years of research.Instead, he moved toward the surface,

creating the HOT program to establishbaselines for various oceanic processesand element cycles (12). During the late1970s and early 1980s, he began teasing

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The C-MORE Hale laboratory.

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apart the rates of various ocean cycles(i.e., carbon, nitrogen, phosphorus) thatKarl says are key to understanding theglobal models of production, fisheries,and climate change (13–15). His studiesrevealed that microbes were key playersin the carbon cycle and the missing link inthe marine food web (16).In the early 1980s, Karl and other

leaders in the field were summoned by theNAS to plan the Global Ocean Flux Study(GOFS), a research prospectus for ex-ploring the ocean’s carbon cycle duringthe next decade.Over the next few years, Karl pitched

ocean time-series measurements as a keycomponent of GOFS, particularly toexplore how microbes sustain nutrientcycles and organic production. The timingwas fortuitous because Charles DavidKeeling’s atmospheric CO2 curve hadgarnered tremendous interest and un-derscored the value of time-series proj-ects. Using measurements taken at theSouth Pole and the Mauna Loa observa-tory since 1958, Keeling had tracked in-creasing concentrations of atmosphericCO2. “If he hadn’t been making thosemeasurements month after month aftermonth, we would never have been able tounderstand the role of CO2 in global cli-mate,” Karl says.To crack the ocean’s carbon cycle, Karl

needed to generate a time series forplankton and biogeochemistry. The studyrequired a team of scientists and en-gineers to make repeat measurements,“which, quite frankly, are pretty boringuntil you get a long time series,” saysKarl. He notes that it was a risky earlycareer move because the research was nothypothesis-driven; rather, it was driven bya “build it and they will come” mentality.He proposed the HOT program to theNSF in 1987.

The HOT program was one of twoproposed GOFS time-series stations, eachcosting 1 million dollars. The proposalswere funded, and the first cruises werelaunched simultaneously in October 1988.In Hawaii, the biogeochemical and eco-logical study was complemented by asystematic study of ocean physics and cli-mate led by Karl’s colleague in Hawaii,Roger Lukas.Originally, the HOT program research

was entirely ship-based, with scientistsgoing out once a month to make obser-vations and conduct experiments over5 days. After a few years, they added amooring, basically a string of instrumentsfrom the seabed to the sea surface thattook more frequent measurements. In2007, the HOT program team launcheda fleet of autonomous “Seagliders,” bat-tery-operated robots capable of data col-lection and transmission back to shore.The two ocean time-series programs

have each produced 23 years’ worth (andcounting) of data that are now recognizedas being equivalent to the Keeling Curveof the ocean. In 2009, Karl and his col-leagues published data from the HOTprogram in PNAS, proving that the oceanswere becoming more acidic because ofrising atmospheric CO2 levels (1).In his Inaugural Article (17), Karl

and his colleagues in the HOT programdescribe the marine biological carbonpump and its role in deep-sea carbon se-questration. The authors document alarge, annually recurrent sedimentationevent in late summer at their study site inthe Pacific Ocean north of Hawaii. Be-cause oceanographic habitat features varybetween years while export is temporallypredictable, the authors hypothesize thatthe regularity of the massive sedimenta-tion event may be controlled by daylength, a general phenomena known as

photoperiodism. The results underscorehow little we know about some of themost fundamental ecological processeson Earth.

Time Series and C-MOREToday, Karl has taken on an even biggerventure as director of C-MORE, a part-nership between the University of Hawaiiand collaborators at five US mainlandinstitutions.Karl describes C-MORE as a “super-

HOT program.” It is based at the HOTStation ALOHA and complements theHOT program with more variables, in-cluding genomics measurements. Thegoal will be to “understand the dynamicsof life in the sea, from the genome tothe biome”: how the ocean and marinelife respond to habitat changes, bothnatural and human-made. The pièce derésistance will be the 6-month mannedoccupation of Station ALOHA using an80-ft ex-military ship that Karl plans toreconfigure as a remote laboratory. “It’sgoing to be a one-of-a-kind dataset, agold mine for knowledge creation anddissemination,” says Karl. A new researchfacility, C-MORE Hale, has recentlybeen constructed on the Universityof Hawaii campus to support the re-search mission.Although Karl is not going on as many

research expeditions as he used to, hehas logged more than 1,000 days at seain his career and is adamant that he hasnot retired, just shifted responsibilities.“I would like to think of my role, espe-cially in the last 5 years, as being a sciencefacilitator and opportunity broker. Formy entire scientific career, I have beenthe beneficiary; it is time to give back,”states Karl.

Bijal P. Trivedi, Freelance Science Writer

1. Dore JE, Lukas R, Sadler DW, Church MJ, Karl DM(2009) Physical and biogeochemical modulation ofocean acidification in the central North Pacific. ProcNatl Acad Sci USA 106:12235–12240.

2. Clarke AC (1966) The Challenge of the Sea (MayflowerBooks, London).

3. Karl DM (1978) Distribution, abundance and metabolicstates of microorganisms in the water column andsediments of the Black Sea. Limnol Oceanogr 23:936–949.

4. Karl DM (1993) Microbial processes in the SouthernOcean. Antarctic Microbiology, ed Friedmann EI (Wi-ley, New York), pp 1–63.

5. Karl DM, et al. (1999) Microorganisms in the accretedice of Lake Vostok, Antarctica. Science 286:2144–2147.

6. Karl DM, LaRock PA (1975) Adenosine triphosphatemeasurements in soil and marine sediments. J Fish ResBoard Can 32:599–607.

7. Karl DM, Dobbs FC (1998) Molecular approaches tomicrobial biomass estimation in the sea. MolecularApproaches to the Study of the Ocean, ed Cooksey KE(Chapman & Hall, London), pp 29–89.

8. Karl DM (2007) Microbial oceanography: Paradigms,processes and promise. Nat Rev Microbiol 5:759–769.

9. Karl DM, Wirsen CO, Jannasch HW (1980) Deep-seaprimary production at the Galapagos hydrothermalvents. Science 207:1345–1347.

10. Karl DM, McMurtry GM, Malahoff A, Garcia MO (1988)Loihi Seamount, Hawaii: A mid-plate volcano witha distinctive hydrothermal system. Nature 335:532–535.

11. Karl DM (1995) Ecology of free-living, hydrothermalvent microbial communities. The Microbiology ofDeep-Sea Hydrothermal Vents, ed Karl DM (CRC, BocaRaton, FL), pp 35–124.

12. Karl DM, Lukas R (1996) The Hawaii Ocean Time-series

(HOT) Program: Background, rationale and field im-

plementation. Deep-Sea Res 43:129–156.13. Karl DM (1999) A sea of change: Biogeochemical vari-

ability in the North Pacific subtropical gyre. Ecosystems

(NY) 2:181–214.14. Karl D, et al. (2002) Dinitrogen fixation in the world’s

oceans. Biogeochemistry 57/58:47–98.15. Karl D, et al. (1997) The role of nitrogen fixation in

biogeochemical cycling in the subtropical North Pacific

Ocean. Nature 388:533–538.16. Karl DM (2000) Aquatic ecology: Phosphorus, the staff

of life. Nature 406:31–33.17. Karl DM et al. (2012) Predictable and efficient carbon

sequestration in the North Pacific Ocean supported by

symbiotic nitrogen fixation. Proc Natl Acad Sci USA

109:1842–1849.

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