1,720,996 research outputs found
The Bermuda Atlantic Time-series Study (BATS) enters its twenty-fifth year of ocean observations in the North Atlantic that illustrate change in ocean carbon
No full textMeasuring ocean change : results from BATS, HOT, and CARIACO
No full textPicophytoplankton carbon biomass at the Bermuda Atlantic Time-series Study (BATS) site from June 2004 to December 2010 was estimated from the direct calibration of cellular carbon content and forward light scatter (via flow cytometry). Seasonality and interannual dynamics of Prochlorococcus, Synechococcus and small eukaryotic algae (<12 mu m diameter) abundance, cellular carbon content (Q(C); particulate organic carbon; POC cell(-1)), and group-specific carbon biomass are reported. Q(C) of individual taxa varied with depth and season by as much as an order of magnitude, roughly comparable to variability in abundance. During the time-series there were obvious shifts in the taxonomic distribution of photosynthetic carbon biomass; these interannual shifts in biomass were due to simultaneous changes in both Q(C) and cell abundance. The observed pattern was not apparent from numerical abundance alone, highlighting the importance of Q(C) measurements in place of using fixed conversion factors to better understand biological carbon dynamics. Changes in the phase of the North Atlantic Oscillation (NAO) from positive to negative modes correlated with shifts in biomass between picocyanobacteria and small eukaryotic algae, respectively. Thus, shifts in algal community structure are inferred to be associated with changes in light intensity and implied nutrient supply via mixing (i.e., patterns in upper ocean stability). These observed changes in phytoplankton biomass partitioning were correlated with the important ocean carbon cycle parameters of export flux, mesopelagic transfer efficiency, and elemental stoichiometry. Importantly, interannual relationships between these parameters and algal biomass were detected only when Q(C) was considered as variable
Microbial productivity of the Sargasso Sea and how it compares to elsewhere, and the role of the Sargasso Sea in carbon sequestration – better than carbon neutral?
No full textRevisiting N2 fixation in the North Atlantic Ocean: Significance of deviations from the Redfield Ratio, atmospheric deposition and climate variability
No full textThe average oceanic nitrate-to-phosphate molar ratio (NO3?:PO43??16:1, referred to as the Redfield Ratio) in subsurface waters, which is similar to the average ratio of particulate nitrogen (N)-to-phosphorus (P) in phytoplankton, is the cornerstone in calculating geochemical estimates of N2 fixation and denitrification rates. Any deviations from this canonical Redfield Ratio in intermediate ocean waters, expressed as N* (a measure of NO3? in excess or deficit of 16×PO43?), provides an integrated estimate of net N fluxes into and out of the ocean. In well-oxygenated ocean basins such as the North Atlantic Ocean, N* estimates are usually positive and can be used to infer that rates of N2 fixation exceed rates of denitrification. We use this approach to estimate N2 fixation over the last two decades (1988–2009) based on data collected at the Bermuda Atlantic Time-series Study (BATS) site in the North Atlantic Ocean near Bermuda. Our results indicate that interpretation of the N* tracer as an estimate of N2 fixation should be undertaken with caution, as N2 fixation is not the only process that results in a positive N* estimate. The impacts of a locally variable nitrogen-to-phosphorus ratio, relative to the fixed Redfield Ratio, in the suspended particulate matter as well as in the subsurface water nutrients and atmospheric N deposition on N* variability were examined. Furthermore, we explored the role of climate modes (i.e., North Atlantic Oscillation and Arctic Oscillation) on N* variability. We found that N* in the subsurface waters was significantly affected by these factors and hence previous estimates of N2 fixation using this technique might have been substantially overestimated. Our revised estimate of N2 fixation in the North Atlantic Ocean (0°N–50°N, 20°W–80°W) is 12.2±0.9×1011 mol N yr?1, and based on long-term BATS data provides better constraints than both earlier indirect and direct estimates N2 fixation
Two decades and counting: 24-years of sustained open ocean biogeochemical measurements in the Sargasso Sea
No full textThe Bermuda Atlantic Time-series Study (BATS) program has sampled the northwestern Sargasso Sea on a biweekly (January to April) to monthly basis since October 1988. The primary objective of the core BATS program continues to be an improved understanding of the time-variable processes and mechanisms that control the biogeochemical cycling of carbon and related elements in the surface ocean. With 24 years of measurements for most chemical, physical and biological variables, we have moved beyond descriptions of seasonal and interannual variability to examination of multi-year trends and potential controls, however there remain substantial gaps in our knowledge of the ecosystem mechanisms related to organic matter production, export and remineralization. While earlier BATS overviews have focused on describing seasonal and year-to-year variability, this overview provides new information on three long-standing biogeochemical questions in Sargasso Sea biogeochemistry. First, why is there a discrepancy between biological (i.e., sediment trap) and geochemical estimates of carbon export production? Winter storms and mesoscale eddies have now been clearly shown to contribute to annual nutrient budgets and carbon export production. Recent information on phytoplankton natural isotopic nitrogen composition, and data from profiling floats suggests that small phytoplankton are important contributors to new production in summer despite the apparent absence of a mechanism to entrain nitrate into the euphotic zone. These findings aid in closing the gap between these two different estimates of carbon export production. Second, what supports the seasonal drawdown of carbon dioxide in the absence of detectable nutrients? The zooplankton timeseries at BATS highlights the importance of zooplankton as a conduit for carbon removal due to grazing and vertical migration. Although increases in cellular elemental stoichiometry to values greater than the canonical Redfield Ratio, and the seasonal (and interannual) accumulation of euphotic zone dissolved organic carbon (DOC) without accumulation of DON in the surface ocean are also important explanations. Lastly, what are the sources of the elevated nitrate to phosphate ratio in the seasonal thermocline (N:P>30 on average)? While generally accepted that nitrogen fixation is the source of the additional nitrogen, new research suggests that export and remineralization of non-diazotroph particulate matter enriched in nitrogen (alternatively viewed as depleted in phosphorus) may also make substantial contributions. In addition, the ratio of particulate nitrogen to phosphorus captured in sediment traps has decreased from 50–75 to <50, possibly due to enhanced nitrogen remineralization. These and other findings from the core BATS observational program contribute to our improved understanding of biogeochemical cycles and ecosystem mechanisms in the subtropical North Atlantic Ocean and how they are changing over time
Biogeochemical responses to late-winter storms in the Sargasso Sea. IV. Rapid succession of major phytoplankton groups
No full textIn this paper, we present multi-parameter data on phytoplankton community composition, and its response to storm events in the Sargasso Sea in late February and early March of 2 years (2004 and 2005). Observed physical conditions spanned a continuum from pulsed destratification/stratification to continuous mixing, with a corresponding range of phytoplankton growth responses. The pulsed destratification/stratification condition resulted in a rapid (1–2 d) doubling of euphotic zone chlorophyll (Chl-a) along with a rapid succession, days timescale, from diatoms to haptophytes and then to cyanobacteria. Deep (>300 m) continuous mixing led to a slow (8–9 d) doubling of autotrophic biomass with no observed succession in the phytoplankton community. These different temporal responses appear to be due to differences between nutrient-limited and light-limited phytoplankton growth, although differences in grazing rates or selective grazing cannot be ruled out. Unexpectedly, we found that flow cytometrically enumerated picoeukaryotes were not accounted for in HPLC-pigment derived phytoplankton classifications and did not covary with any of the pigments quantified. Yet, the picoeukaryotes were positively related to increases in total Chl-a and increased carbon export, suggesting an important but as yet unknown role in the Sargasso Sea carbon cycle
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