Characterizing Limits of Precision for Dissolved Organic Nitrogen Calculations

Saunders, James F.; Yu, Yun; McCutchan, James H.; Rosario‐Ortiz, Fernando L.

doi:10.1021/acs.estlett.7b00416

Cited by 15 publications

(1 citation statement)

References 23 publications

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“…Water samples were filtered on board upon collection to separate dissolved material (DOC, DON and inorganic nutrients) from particulate material (POC and PON). Filters and most of the filtration unit were combusted in a muffle furnace before use (Kaplan, 1992;Sharp et al, 1993). Gentle vacuum filtration (∼ 5 kPa) was used through pre-combusted (450 • C, 5 h) 47 mm diameter glass fibre filters of nominal pore size 0.7 µm (GF/F) with an ashed (550 • C, 5 h) glass filtration unit.…”

Section: Analytical Proceduresmentioning

confidence: 99%

Interannual variability in the summer dissolved organic matter inventory of the North Sea: implications for the continental shelf pump

2019

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Abstract. We present the distribution and C:N stoichiometry of dissolved organic matter (DOM) in the North Sea in two summers (August 2011 and August 2012), with supporting data from the intervening winter (January 2012). These data demonstrate local variability superimposed on a general pattern of decreasing DOM with increasing distance from land, suggesting concentrations of DOM are controlled on large spatial scales by mixing between the open North Atlantic and either riverine sources or high DOM productivity in nearshore coastal waters driven by riverine nutrient discharge. Given the large size and long residence time of water in the North Sea, we find concentrations are commonly modified from simple conservative mixing between two endmembers. We observe differences in dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations and land–ocean gradients between the two summers, leading to an estimated 10–20 Tg difference in the DOC inventory between the two years, which is of the same order of magnitude as the annual uptake of atmospheric CO2 by the North Sea system, and thus significant for the carbon budget of the North Sea. This difference is not consistent with additional terrestrial loading and is more likely to be due to balancing of mixing and in situ production and loss processes across the North Sea. Differences were particularly pronounced in the bottom layer of the seasonally stratifying northern North Sea, with higher DOC and C:N ratio in 2011 than in 2012. Using other data, we consider the extent to which these differences in the concentrations and C:N ratio of DOM could be due to changes in the biogeochemistry or physical circulation in the two years, or a combination of both. The evidence we have is consistent with a flushing event in winter 2011/12 exchanging DOM-rich, high C:N shelf waters, which may have accumulated over more than 1 year, with deep North Atlantic waters with lower DOC and marginally higher DON. We discuss the implications of these observations for the shelf sea carbon pump and the export of carbon-rich organic matter off the shelf and hypothesise that intermittent flushing of temperate shelf systems may be a key mechanism in the maintenance of the continental shelf pump, via the accumulation and subsequent export of carbon-rich DOM.

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Section: Analytical Proceduresmentioning

confidence: 99%