Ocean Carbon and Biogeochemistry (OCB) Summer Workshop Woods Hole Oceanographic Institution July 25-28, 2016
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Ocean Carbon and Biogeochemistry (OCB) Summer Workshop Woods Hole Oceanographic Institution July 25-28, 2016 POSTER ABSTRACTS Diatom community composition shifts in response to eddies in the California coastal transition zone Z. M. Abdala1, S. Einarsson1, K. Powell1, J. Fitzsimmons2, T. Coale3, C. P. Till4, P. D. Chappell1 1. Old Dominion University, [email protected] 2. Texas A&M University 3. University of California San Diego 4. University of California Santa Cruz Diatoms are photosynthetic, unicellular, planktonic organisms that rely on nutrient availability and play a fundamental role in global ecosystems. Community structures and distributions of these important phytoplankton will fluctuate for many reasons, but in the California current upwelling regime, nutrient circulation (especially nitrate and iron) is thought to be a major determining factor in diatom abundance. Samples collected along a transect that passed through two sea surface height anomalies were analyzed for diatom community composition changes. Community composition was found to shift rapidly in response to the physical forcing manipulating nutrient availability. Communities from the offshore anomaly were found to be mostly dominated by a single Rhizosolenia species, whereas surrounding areas were comprised of a variety of different diatoms. The diatom community data is being analyzed in the context of nutrient and physical data to speculate on what factors were potentially responsible for the shifts in composition. Phytoplankton biogeography, primary productivity and nitrogen uptake in the ultra-oligotrophic Indian Ocean S. E. Baer1, S. Rauschenberg1, A. Steinberger3, A. C. Martiny2, B. S. Twining1, M. W. Lomas1 1. Bigelow Laboratory for Ocean Sciences 2. University of California, Irvine 3. Williams College Biogeochemical data from the central Indian Ocean is currently limited, but it is known that there are stark geographical gradients in the physical and chemical conditions that may lead to unique biogeochemical regimes. As participants on the IO9N GO-SHIP cruise, a transect from 28ºS to 18ºN in the Indian Ocean completed in spring of 2016, samples for nutrient uptake and phytoplankton cell counts were obtained at approximately every other degree of latitude. Stable isotopically labeled 13C-bicarbonate was used to measure primary productivity and 15N labeled nitrate, ammonium, and urea to measure uptake of nitrogen compounds in near surface waters (~20 m). Nitrate and phosphate concentrations were below detection limits throughout the surface 50 m, while ammonium was undetectable at all stations and depths measured. Below ~50 m, nitrate and phosphate concentrations steadily increased from south to north, to a maximum of 31 and 2.2 µM respectively, with their supply ratio (N:P) always below 15. Absolute uptake rates of all N compounds were less than 1.5 nmol N L-1 h-1 south of 15°S, and steadily increased until highest observed values were reached between 1.5-6.5°N; 1.8, 5.2, and 5.1 nmol N L-1 h-1 for nitrate, ammonium, and urea respectively. In the Bay of Bengal (10- 18°N), uptake rates were not variable, with a mean of 0.86, 3.2, and 3.1 nmol N L-1 h-1 for nitrate, ammonium, and urea respectively. Ammonium and urea uptake rates were consistently 3-5 times higher than concurrent nitrate uptake rates, with a mean observed f-ratio of 0.23 for the entire transect. Rates of primary production followed the same general trend of nitrogen uptake, with a maximum of 77.8 nmol C L-1 h-1. Cell counts by flow cytometry indicate that at all stations and depths, heterotrophic bacteria dominated in both numerical abundance and biomass. Prochlorococcus was the dominant phytoplankton group, but with increasing contributions of Synechococcus and small eukaryotes from south to north. This data represents the first reported direct measurements of primary production, nitrogen uptake, and phytoplankton abundance in the eastern central Indian Ocean, a large but relatively understudied region of the global ocean. Relative roles of dissolution lengthscale and uptake ratio in the global distribution of silicate R. Bernardello1, M. C. Moore2, A. P. Martin1 1. National Oceanography Centre Southampton 2. Ocean and Earth Science, University of Southampton We investigate controls on the global distribution of silicate with a coupled physical- biogeochemical model using a set of experiments designed to test the sensitivity of an idealized non-limiting nutrient (Xnu). In a fixed steady-state circulation dissolution lengthscale for Xnu and its uptake ratio by phytoplankton with respect to phosphate were varied across a wide range and over different regions. Steady state solutions for Xnu were then compared with observed climatological silicate. Both deep dissolution and high uptake ratio were able to cause the sharp meridional gradient observed for silicate at the surface of the Southern Ocean. However, only the former was able to determine the meridional gradient in concentration between the deep North Pacific and the deep Southern Ocean. Experiments with regional variations in the two parameters revealed an important role for the deep dissolution in the North Pacific, pointing to locally recycled silicate being determinant in the build-up of deep silicate. Although it's not possible to tell which of the two studied processes is the main driver in the Southern Ocean, only a deep dissolution lengthscale was able to reproduce both main characteristics of the global silicate distribution. We speculate that the high uptake ratio of silicate with respect to other macro-nutrients observed in the Southern Ocean would then be only a consequence (rather than a driver) of the high surface silicate concentration. The local and remote influences of remineralization in setting global nutrient distributions R. Bernardello1, A. Martin1, S. Henson1, A. Yool1, S. Khatiwala2, I. Kriest3, M. Moore4, J. Blundell4, J. Dunne5, I. Allen6, I. Totterdell7. 1. National Oceanography Centre Southampton 2. University of Oxford 3. GEOMAR 4. University of Southampton 5. Geophysical Fluid Dynamic Laboratory 6. Plymouth Marine Laboratory 7. Met Office Nutrient concentrations at any depth or location are the sum of organic material that has been remineralised and unused nutrients from the surface (preformed). Even for macro- nutrients, such as phosphate, the relative roles of the biological carbon pump (BCP) and of the ocean circulation in shaping their global distribution are still unclear. The former acts mainly in the vertical dimension while the latter acts to redistribute nutrients in three dimensions. Furthermore, both components act locally and remotely. We use a three- dimensional coupled physical-biogeochemical model to investigate local and remote contributions to steady-state phosphate distribution in a biome-based framework. Remineralised phosphate produced in each biome is tagged and conserved in the interior of the ocean once outside the biome of origin. Two different representations of ocean circulation are used. We find that local remineralisation exerts a limited control on total phosphate contributing only between 2-24% below 1000m depth, depending on the model and biome considered. Even with respect to remineralised phosphate the locally produced fraction reaches only about 45% maximum. When comparing results between the two different circulations important differences are found in some biomes, highlighting the importance of considering uncertainty in circulation. We conclude that nutrient profiles provide a weak constraint on local biogeochemical processes. Carbon Hot Spot: A field program to understand bio-physical drivers of carbon sequestration in western boundary current regions S. P. Bishop1, A. J. Fassbender2, M. F. Cronin2, D. Zhang2,3, R. Inoue4, C. Osburn1, E. Oka5, B. Qiu6, X. Lin7 1. North Carolina State University, [email protected] 2. NOAA/Pacific Marine Environmental Laboratory 3. Joint Institute for the Study of the Atmosphere and Ocean 4. Japan Agency for Marine Earth Science and Technology 5. University of Tokyo 6. University of Hawaii at Manoa 7. Ocean University of China Western Boundary Currents (WBC) are dynamic ocean regions characterized by large air-sea exchanges of heat, moisture, and carbon, and exhibit the highest eddy kinetic energy in the global ocean. As centers of subtropical mode water (STMW) formation, these strong carbon sink zones are thought to account for a majority of anthropogenic carbon sequestered by the ocean outside of the polar deep-water-formation regions, making WBCs hotspots for studying the carbon cycle. Many questions remain about the specific processes driving formation and long-term evolution of STMW in the presence of meso- and submesoscale eddies. Coupled climate models that include biogeochemical (BGC) properties are in their infancy and still rely on parameterizations for mesoscale eddies. In order to adequately make and understand future climate projections, it is pivotal to improve our dynamical understanding of these ocean processes, as well as the accompanying bio-physical interactions that influence marine carbon cycling. The objective of Carbon Hot Spot is to develop an interdisciplinary and international research community that will facilitate better understanding and awareness of the role that WBCs play in climate and anthropogenic carbon sequestration. We hope to achieve this by planning and conducting a field program in the Kuroshio Extension region. In order to foster new collaborations and realize scientific breakthroughs in