The role of nutricline depth in regulating the ocean carbon cycle
Open Access
- 23 December 2008
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 105 (51), 20344-20349
- https://doi.org/10.1073/pnas.0811302106
Abstract
Carbon uptake by marine phytoplankton, and its export as organic matter to the ocean interior (i.e., the “biological pump”), lowers the partial pressure of carbon dioxide (pCO2) in the upper ocean and facilitates the diffusive drawdown of atmospheric CO2. Conversely, precipitation of calcium carbonate by marine planktonic calcifiers such as coccolithophorids increases pCO2 and promotes its outgassing (i.e., the “alkalinity pump”). Over the past ≈100 million years, these two carbon fluxes have been modulated by the relative abundance of diatoms and coccolithophores, resulting in biological feedback on atmospheric CO2 and Earth's climate; yet, the processes determining the relative distribution of these two phytoplankton taxa remain poorly understood. We analyzed phytoplankton community composition in the Atlantic Ocean and show that the distribution of diatoms and coccolithophorids is correlated with the nutricline depth, a proxy of nutrient supply to the upper mixed layer of the ocean. Using this analysis in conjunction with a coupled atmosphere–ocean intermediate complexity model, we predict a dramatic reduction in the nutrient supply to the euphotic layer in the coming century as a result of increased thermal stratification. Our findings indicate that, by altering phytoplankton community composition, this causal relationship may lead to a decreased efficiency of the biological pump in sequestering atmospheric CO2, implying a positive feedback in the climate system. These results provide a mechanistic basis for understanding the connection between upper ocean dynamics, the calcium carbonate-to-organic C production ratio and atmospheric pCO2 variations on time scales ranging from seasonal cycles to geological transitions.Keywords
This publication has 41 references indexed in Scilit:
- Calcium carbonate cycling in future oceans and its influence on future climatesJournal of Plankton Research, 2007
- A rising tide lifts all phytoplankton: Growth response of other phytoplankton taxa in diatom‐dominated bloomsGlobal Biogeochemical Cycles, 2006
- Response of ocean ecosystems to climate warmingGlobal Biogeochemical Cycles, 2004
- Historical climate change and ocean turbulence as selective agents for two key phytoplankton functional groupsMarine Ecology Progress Series, 2004
- Ocean primary production and climate: Global decadal changesGeophysical Research Letters, 2003
- Basin‐wide particulate carbon flux in the Atlantic Ocean: Regional export patterns and potential for atmospheric CO2 sequestrationGlobal Biogeochemical Cycles, 2001
- What caused the glacial/interglacial atmospheric pCO2 cycles?Reviews of Geophysics, 2000
- Hydrostatic, quasi‐hydrostatic, and nonhydrostatic ocean modelingJournal of Geophysical Research: Oceans, 1997
- A finite‐volume, incompressible Navier Stokes model for studies of the ocean on parallel computersJournal of Geophysical Research: Oceans, 1997
- Coccolithophorid blooms in the global oceanJournal of Geophysical Research: Oceans, 1994