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Woods Hole Oceanographic Institution

Kelton McMahon

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Projects
» Historical shifts in plankton communities

» Food web architecture in coral reefs

» Seascape connectivity of reef fish

» Ocean isoscapes

» Ocean-basin scale migrations of large pelagic fishes

» Bivalves as bioproxies for climate change

» Digestibility of Ice Algae and Phytoplankton

» Fundulus heteroclitus


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The North Pacific subtropical gyre (NPSG), shown here, is the largest continuous ecosystem on earth, and a critical regulator of global CO2 and biogeochemical balance. According to recent satellite observations, the NPSG is expanding at a rate of 1-4% per year, commensurate with global decrease in (net) primary productivity. Despite declines in nutrient availability, primary production in the NPSG (Chl a color bar) has actually increased in recent decades counter to the global trend. (Google Earth)



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The deep-sea Hawaiian gold coral Kulamanamana haumeaae (previously known as Gerardia sp.) is an extraordinarily long-lived species, reaching ages of thousands of years.  These proteinaceous  "corals," secrete an endoskeleton of diagenetically-resistant growth layers synthesized from their primary food source, recently exported sinking particles. Thus, these "corals" act as bio-archives akin to living sediment traps, providing unique geochemical time-series at annual to decadal-scale resolution over millenial time scales. Compound-specific stable isotope analysis of these "corals" is being used to reconstruct past changes in NPSG biogeochemical cycling, phytoplankton community dynamics, and export production as a function of decadal to century scale climate change. (NOAA/HURL)


Decadal to centry scale changes in North Pacific Ocean phytoplankton communities assessed by δ13C compound-specific stable isotope analysis of deep-sea corals

Collaborators:
Dr. Mathew McCarthy: University of California - Santa Cruz, Dr. Thomas Guilderson: Lawrence Livermore National Laboratory, Dr. Thomas Larsen: Christian-Albrechts-Universität zu Kiel, Dr. Owen Sherwood: University of Colorado

The North Pacific subtropical gyre (NSPG) is the largest continuous ecosystem on earth, and a critical regulator of global CO2 and biogeochemical balance. Despite declines in nutrient availability, primary production in the NPSG has actually increased in recent decades counter to the global trend. We are analyzing records of bulk and compound-specific carbon isotope data in long-lived, deep-sea proteinaceous corals from the Hawaiian archipelago as a proxy for export production and surface to mesopelagic coupling. After a steady ~1.5‰ enrichment in δ13CBulk values between 1000-1850AD, there has been a dramatic 2‰ depletion in δ13CBulk values since the end of the Little Ice Age much greater than expected from the Seuss Effect alone. Essential amino acid δ13C values, which act as isotopic fingerprints of primary producer origin, show significant concurrent changes over this time period. Our preliminary findings suggest fundamental shifts in ecosystem baseline biogeochemistry potentially connected to a “domain shift” in the NPSG between eukaryotic and prokaryotic community. This change could have widespread ramifications on rates of primary production and export production, biogeochemical processes, and ecosystem function and resilience.


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