Interannual variability in the summer dissolved organic matter inventory of the North Sea: implications for the continental shelf pump
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...
Published in: | Biogeosciences |
---|---|
Main Authors: | , , |
Format: | Text |
Language: | English |
Published: |
2019
|
Subjects: | |
Online Access: | https://doi.org/10.5194/bg-16-1073-2019 https://www.biogeosciences.net/16/1073/2019/ |
id |
ftcopernicus:oai:publications.copernicus.org:bg61606 |
---|---|
record_format |
openpolar |
spelling |
ftcopernicus:oai:publications.copernicus.org:bg61606 2023-05-15T17:32:56+02:00 Interannual variability in the summer dissolved organic matter inventory of the North Sea: implications for the continental shelf pump Chaichana, Saisiri Jickells, Tim Johnson, Martin 2019-03-18 application/pdf https://doi.org/10.5194/bg-16-1073-2019 https://www.biogeosciences.net/16/1073/2019/ eng eng doi:10.5194/bg-16-1073-2019 https://www.biogeosciences.net/16/1073/2019/ eISSN: 1726-4189 Text 2019 ftcopernicus https://doi.org/10.5194/bg-16-1073-2019 2019-12-24T09:49:23Z 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 CO 2 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. Text North Atlantic Copernicus Publications: E-Journals Biogeosciences 16 5 1073 1096 |
institution |
Open Polar |
collection |
Copernicus Publications: E-Journals |
op_collection_id |
ftcopernicus |
language |
English |
description |
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 CO 2 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. |
format |
Text |
author |
Chaichana, Saisiri Jickells, Tim Johnson, Martin |
spellingShingle |
Chaichana, Saisiri Jickells, Tim Johnson, Martin Interannual variability in the summer dissolved organic matter inventory of the North Sea: implications for the continental shelf pump |
author_facet |
Chaichana, Saisiri Jickells, Tim Johnson, Martin |
author_sort |
Chaichana, Saisiri |
title |
Interannual variability in the summer dissolved organic matter inventory of the North Sea: implications for the continental shelf pump |
title_short |
Interannual variability in the summer dissolved organic matter inventory of the North Sea: implications for the continental shelf pump |
title_full |
Interannual variability in the summer dissolved organic matter inventory of the North Sea: implications for the continental shelf pump |
title_fullStr |
Interannual variability in the summer dissolved organic matter inventory of the North Sea: implications for the continental shelf pump |
title_full_unstemmed |
Interannual variability in the summer dissolved organic matter inventory of the North Sea: implications for the continental shelf pump |
title_sort |
interannual variability in the summer dissolved organic matter inventory of the north sea: implications for the continental shelf pump |
publishDate |
2019 |
url |
https://doi.org/10.5194/bg-16-1073-2019 https://www.biogeosciences.net/16/1073/2019/ |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
eISSN: 1726-4189 |
op_relation |
doi:10.5194/bg-16-1073-2019 https://www.biogeosciences.net/16/1073/2019/ |
op_doi |
https://doi.org/10.5194/bg-16-1073-2019 |
container_title |
Biogeosciences |
container_volume |
16 |
container_issue |
5 |
container_start_page |
1073 |
op_container_end_page |
1096 |
_version_ |
1766131266683404288 |