Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

Biogeochemical and biological data collected on the Trophic BATS cruises in the Sargasso Sea. Data are from 4 cruises over the span 2011-2012. The provided data are complete matrices and therefore not every sample (columns) will be taken from every Niskin fired (rows).

Methods are summarized below. Detailed methods for all data collected as part of this study can be found in the publications arising from this study (references given below).

On each BATS cruise, aquasi-lagrangian sampling scheme is employed. An in situ primary productivity array is deployed from dawn to dusk. The biogeochemistry and biological parameters reported in this data were measured from Niskin bottle water samples.

Bacterial production was measured using [3H-methyl] thymidine incorporation and converted to carbon-based bacterial production using standard equations. Bacterial abundance was determined using DAPI stained epifluorescence microscopy. Pico-autotrophs were identified as either Synechococcus and Prochlorococcus.

Samples for NO3/NO2, NO2 and PO4 are filtered and frozen (-20 degrees C) in HDPE bottles until analysis. Total organic carbon (TOC) and total nitrogen were determined using high temperature combustion techniques. Total phosphorus concentrations are quantified using a high temperature/persulfateoxidation technique. Particulate organic carbon (POC) and nitrogen (PON) samples were filtered on precombusted Whatman GF/F filters and frozen until analysis on an elemental analyzer. Particulate phosphorus samples were analyzed using an ash-hydrolysis method with oxidation efficiency and standard recovery checks.

Sample QA/QC procedures followed those given in the associated manuscripts. At the point of collection, any leaking niskin bottles were noted on the master cast sheets and samples were taken from a different niskin fired at the same depth as the leaking bottle. No data are reported for leaking Niskin bottles. During sample analysis, certified standards, where available, were carefully examined to ensure that they were consistent with expectations for accuracy and precision. If no obvious error or problem was found, the data were considered OK and in the range of environmental data that this study hoped to observe.

Sample accuracy was assessed by using certified standards, for those measurements where standards are available. Certified standards were run with each analytical run and compared to long term control charts for respective analyses. For those analyses where there are no standards (e.g., flow cytometric cell counts) data were assessed for reasonableness based upon extensive experience of the PI’s.

Detailed information on analyses:
Lomas, M.W., Burke, A., Lomas, D.A., Bell, D.W., Shen, C., Ammerman, J.W., Dyhrman, S.T. 2010.  Sargasso Sea phosphorus biogeochemistry: An important role for dissolved organic phosphorus (DOP). Biogeosciences 7: 695-710. doi: 10.5194/bg-7-695-2010
Lomas, M.W., Bates, N.R., Johnson, R.J., Knap, A.H., Steinberg, D.K., Carlson, C.A. 2013. Two decades and counting: overview of 24-years of sustained open ocean biogeochemical measurements. Deep Sea Research II doi: 10.1016/j.dsr2.2013.01.008.

References:
Casey, J.R., Aucan, J.P., Goldberg, S.R., and Lomas, M.W. 2013. Changes in partitioning of carbon amongst photosynthetic pico- and nano-plankton groups in the Sargasso Sea in response to changes in the North Atlantic Oscillation. Deep Sea Research II doi: 10.1016/j.dsr2.2013.02.002

The provided data are complete matrices and therefore not every sample (columns) will be taken from every Niskin fired (rows). Data that were either not collected, or were associated with leaking Niskins, or were found to be in error for other reasons are denoted by 'nd'. Most of the data given in this dataset are not derived variables and are calculated using reasonably standard equations as given in the appropriate references. Where data are derived (e.g., bacterial carbon biomass) the appropriate reference is given in the parameter definition.

Only nutrient analyses were close to analytical method detection limits (MDL). MDLs were estimated as 3x the standard deviation of the lowest standard used for the analysis and are ~30nM for nitrate and phosphate using a standard autoanalyzer. We used the MAGIC co-precipitation method for phosphate which lowered our MDL to ~0.5nM. Samples below the MDL are reported as the MDL.

BCO-DMO Processing Notes:
- Modified parameter names to conform with BCO-DMO naming conventions.
- Replaced '-9.99' with 'nd'.

Fluxes of particulate carbon from the surface ocean are greatly influenced by the size, taxonomic composition and trophic interactions of the resident planktonic community. Large and/or heavily-ballasted phytoplankton such as diatoms and coccolithophores are key contributors to carbon export due to their high sinking rates and direct routes of export through large zooplankton. The potential contributions of small, unballasted phytoplankton, through aggregation and/or trophic re-packaging, have been recognized more recently. This recognition comes as direct observations in the field show unexpected trends. In the Sargasso Sea, for example, shallow carbon export has increased in the last decade but the corresponding shift in phytoplankton community composition during this time has not been towards larger cells like diatoms. Instead, the abundance of the picoplanktonic cyanobacterium, Synechococccus, has increased significantly. The trophic pathways that link the increased abundance of Synechococcus to carbon export have not been characterized. These observations helped to frame the overarching research question, "How do plankton size, community composition and trophic interactions modify carbon export from the euphotic zone". Since small phytoplankton are responsible for the majority of primary production in oligotrophic subtropical gyres, the trophic interactions that include them must be characterized in order to achieve a mechanistic understanding of the function of the biological pump in the oligotrophic regions of the ocean.

This requires a complete characterization of the major organisms and their rates of production and consumption. Accordingly, the research objectives are: 1) to characterize (qualitatively and quantitatively) trophic interactions between major plankton groups in the euphotic zone and rates of, and contributors to, carbon export and 2) to develop a constrained food web model, based on these data, that will allow us to better understand current and predict near-future patterns in export production in the Sargasso Sea.

The investigators will use a combination of field-based process studies and food web modeling to quantify rates of carbon exchange between key components of the ecosystem at the Bermuda Atlantic Time-series Study (BATS) site. Measurements will include a novel DNA-based approach to characterizing and quantifying planktonic contributors to carbon export. The well-documented seasonal variability at BATS and the occurrence of mesoscale eddies will be used as a natural laboratory in which to study ecosystems of different structure. This study is unique in that it aims to characterize multiple food web interactions and carbon export simultaneously and over similar time and space scales. A key strength of the proposed research is also the tight connection and feedback between the data collection and modeling components.

Characterizing the complex interactions between the biological community and export production is critical for predicting changes in phytoplankton species dominance, trophic relationships and export production that might occur under scenarios of climate-related changes in ocean circulation and mixing. The results from this research may also contribute to understanding of the biological mechanisms that drive current regional to basin scale variability in carbon export in oligotrophic gyres.

The Ocean Carbon and Biogeochemistry (OCB) program focuses on the ocean's role as a component of the global Earth system, bringing together research in geochemistry, ocean physics, and ecology that inform on and advance our understanding of ocean biogeochemistry. The overall program goals are to promote, plan, and coordinate collaborative, multidisciplinary research opportunities within the U.S. research community and with international partners. Important OCB-related activities currently include: the Ocean Carbon and Climate Change (OCCC) and the North American Carbon Program (NACP); U.S. contributions to IMBER, SOLAS, CARBOOCEAN; and numerous U.S. single-investigator and medium-size research projects funded by U.S. federal agencies including NASA, NOAA, and NSF.

The scientific mission of OCB is to study the evolving role of the ocean in the global carbon cycle, in the face of environmental variability and change through studies of marine biogeochemical cycles and associated ecosystems.

The overarching OCB science themes include improved understanding and prediction of: 1) oceanic uptake and release of atmospheric CO2 and other greenhouse gases and 2) environmental sensitivities of biogeochemical cycles, marine ecosystems, and interactions between the two.

The OCB Research Priorities (updated January 2012) include: ocean acidification; terrestrial/coastal carbon fluxes and exchanges; climate sensitivities of and change in ecosystem structure and associated impacts on biogeochemical cycles; mesopelagic ecological and biogeochemical interactions; benthic-pelagic feedbacks on biogeochemical cycles; ocean carbon uptake and storage; and expanding low-oxygen conditions in the coastal and open oceans.