Influence of winter ventilation on the strength and efficiency of the biological pump
In my postdoctoral research at the Woods Hole Oceanographic Institution, I am testing the mechanistic coupling between physical processes and the biological pump by using biogeochemical models and measurements from autonomous chemical sensors in the North Atlantic. There are currently few locations with year-round time-series measurements of carbon cycle processes in the high latitude oceans, regions where the winter mixing influences I previously identified as strongly influencing the biological pump are likely to have a large effect.
I am currently analyzing data from the new NSF-funded Ocean Observatories Initiative (OOI) array of sensors on moorings and autonomous robotic vehicles in the North Atlantic. These data include measurements of dissolved oxygen, nitrate, and inorganic carbon tracers that I am using to determine the annual rate and efficiency of the biological pump, and its role in driving ocean carbon uptake. I am also combining these observational data with biogeochemical models to develop and test new mechanistic models of the relative influences of physics and biology on export rates and efficiency.
Palevsky, H. I. and D. P. Nicholson (2018), The North Atlantic biological pump: Insights from the Ocean Observatories Initiative Irminger Sea Array. Oceanography, 31(1):42-49, https://doi.org/10.5670/oceanog.2018.108.
The North Pacific biological pump: Rates, efficiency and influence on ocean uptake of carbon dioxide
The North Pacific features a band of strong atmospheric carbon dioxide uptake at the transition between the subarctic and subtropical gyres, making it a region of particular interest to quantify the mechanisms of ocean carbon uptake. Along with other members of the Quay research group at the University of Washington, I measured the the surface concentration of dissolved inorganic carbon (DIC), the partial pressure of carbon dioxide to determine air-sea carbon dioxide flux, and triple oxygen isotopes and oxygen/argon dissolved gas ratios as non-incubation based geochemical tracers of gross primary production and net community production on sixteen container ship transects across the North Pacific between Hong Kong and Long Beach, CA from 2008-2012. My PhD dissertation assesses the rates and efficiency of biological carbon export and evaluates the relative roles of biology, physical circulation, and temperature-driven solubility changes in driving air-sea carbon dioxide flux throughout the full annual cycle across the North Pacific basin (35°N – 50°N, 142°E – 125°W) by constructing mixed layer carbon and oxygen budgets that account for physical and biological influences on the measured tracers.
Palevsky, H. I., P. D. Quay, D. E. Lockwood, and D. P. Nicholson (2016), The annual cycle of gross primary production, net community production and export efficiency across the North Pacific Ocean, Global Biogeochemical Cycles, 29, doi: 10.1002/2015GB005318.
Palevsky, H. I. and P. D. Quay (2017), Influence of the biological pump on ocean carbon uptake over the annual cycle across the North Pacific Ocean, Global Biogeochemical Cycles, 31, 81-95, doi: 10.1002/2016GB005527.
Satellite algorithms and global biogeochemical models as tools to estimate primary and export production: A comparison with geochemical methods
Due to the scarcity of geochemical measurements with broad spatial and temporal coverage such as those in my dissertation work, current global-scale estimates of the strength and efficiency of the biological pump rely on dynamic numerical ocean models with biogeochemical and marine ecosystem components, or empirically-derived models based on satellite observations of ocean temperature and sea surface color. While these are promising tools, few independent direct observational estimates have been available to validate model predictions. I compared chemical tracer-based estimates of photosynthetic production and carbon export rates in the North Pacific with multiple commonly-used model estimates, and found that no single satellite algorithm or model can reproduce seasonal and annual geochemically-determined primary and net community production rates throughout the North Pacific basin. The high latitude regions show large primary production discrepancies in winter and spring and strong effects of deep winter mixed layers on annual net community production that cannot be accounted for in current satellite-based approaches. These results underscore the need to evaluate satellite- and model-based estimates using multiple productivity parameters measured over broad ocean regions and throughout the full annual cycle, including during winter ventilation, in order to accurately estimate the rate and efficiency of carbon sequestration via the ocean’s biological pump.
Palevsky, H. I., P. D. Quay, and D. P. Nicholson (2016), Discrepant estimates of primary and export production from satellite algorithms, a biogeochemical model, and geochemical tracer measurements in the North Pacific Ocean, Geophysical Research Letters, 43, doi:10.1002/2016GL070226.
Fine-scale structure of phytoplankton communities and their role in biological carbon export and ocean carbon uptake
I use novel fine spatial-scale applications of flow cytometry, which identifies phytoplankton populations, and continuous underway dissolved gas measurements, which can be used to quantify the rate and efficiency of biological carbon export to try to better understand the mechanisms that control the biological pump. For my master's research, I used these methods in the Gulf of Alaska to identify a hot spot of intense biological carbon export and oceanic carbon dioxide uptake characterized by a phytoplankton community distinct from the phytoplankton in surrounding regions, indicating the potential significance of both fine-spatial scale processes and of unique phytoplankton assemblages in driving the biological pump.
Palevsky, H. I., F. Ribalet, J. E. Swalwell, C. E. Cosca, E. D. Cokelet, R. A. Feely, E. V. Armbrust, P. D. Quay (2013) The influence of net community production and phytoplankton community structure on CO2 uptake in the Gulf of Alaska. Global Biogeochemical Cycles, 27, 664-676, doi: 10.1002/gbc.20058. [pdf]
Inside the Atlantic Cod Fishery: In Search of a Sustainable Future
I traveled to Iceland, Denmark, Scotland, Norway and Newfoundland to study fisheries science, the fishing industry, and management policies as a Thomas J. Watson Fellow. This project included two fisheries research cruises, one with the Marine Research Institute of Iceland's Northern Shrimp Survey and one with the Scottish Fisheries Research Services as part of the International Bottom Trawl Survey, and first-hand research in fishing communities while living in the homes of fishing families in Peterhead, Scotland, the Lofoten Islands of Norway and Fogo Island, Newfoundland. I also contributed to a published book chapter on European fisheries policy in collaboration with researchers in Denmark and Norway. You can read full details of my experience from my fellowship blog.