The impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the Laptev and East Siberian seas (Siberian Arctic)
Permafrost degradation in the catchment of major Siberian rivers, combined with higher precipitation in a warming climate, could increase the flux of terrestrially derived dissolved organic matter (tDOM) into the Arctic Ocean (AO). Each year, ∼ 7.9 Tg of dissolved organic carbon (DOC) is discharged...
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ftcopernicus:oai:publications.copernicus.org:bg91673 2023-05-15T14:57:24+02:00 The impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the Laptev and East Siberian seas (Siberian Arctic) Hölemann, Jens A. Juhls, Bennet Bauch, Dorothea Janout, Markus Koch, Boris P. Heim, Birgit 2021-06-18 application/pdf https://doi.org/10.5194/bg-18-3637-2021 https://bg.copernicus.org/articles/18/3637/2021/ eng eng doi:10.5194/bg-18-3637-2021 https://bg.copernicus.org/articles/18/3637/2021/ eISSN: 1726-4189 Text 2021 ftcopernicus https://doi.org/10.5194/bg-18-3637-2021 2021-06-21T16:22:14Z Permafrost degradation in the catchment of major Siberian rivers, combined with higher precipitation in a warming climate, could increase the flux of terrestrially derived dissolved organic matter (tDOM) into the Arctic Ocean (AO). Each year, ∼ 7.9 Tg of dissolved organic carbon (DOC) is discharged into the AO via the three largest rivers that flow into the Laptev Sea (LS) and East Siberian Sea (ESS). A significant proportion of this tDOM-rich river water undergoes at least one freeze–melt cycle in the land-fast ice that forms along the coast of the Laptev and East Siberian seas in winter. To better understand how growth and melting of land-fast ice affect dissolved organic matter (DOM) dynamics in the LS and ESS, we determined DOC concentrations and the optical properties of coloured dissolved organic matter (CDOM) in sea ice, river water and seawater. The data set, covering different seasons over a 9-year period (2010–2019), was complemented by oceanographic measurements ( T , S ) and determination of the oxygen isotope composition of the seawater. Although removal of tDOM cannot be ruled out, our study suggests that conservative mixing of high-tDOM river water and sea-ice meltwater with low-tDOM seawater is the major factor controlling the surface distribution of tDOM in the LS and ESS. A case study based on data from winter 2012 and spring 2014 reveals that the mixing of about 273 km 3 of low-tDOM land-fast-ice meltwater (containing ∼ 0.3 Tg DOC) with more than 200 km 3 of high-tDOM Lena River water discharged during the spring freshet ( ∼ 2.8 Tg DOC yr −1 ) plays a dominant role in this respect. The mixing of the two low-salinity surface water masses is possible because the meltwater and the river water of the spring freshet flow into the southeastern LS at the same time every year (May–July). In addition, budget calculations indicate that in the course of the growth of land-fast ice in the southeastern LS, ∼ 1.2 Tg DOC yr −1 ( ± 0.54 Tg) can be expelled from the growing ice in winter, together with brines. These DOC-rich brines can then be transported across the shelves into the Arctic halocline and the Transpolar Drift Current flowing from the Siberian Shelf towards Greenland. The study of dissolved organic matter dynamics in the AO is important not only to decipher the Arctic carbon cycle but also because CDOM regulates physical processes such as radiative forcing in the upper ocean, which has important effects on sea surface temperature, water column stratification, biological productivity and UV penetration. Text Arctic Arctic Ocean East Siberian Sea Greenland Ice laptev Laptev Sea lena river permafrost Sea ice Copernicus Publications: E-Journals Arctic Arctic Ocean East Siberian Sea ENVELOPE(166.000,166.000,74.000,74.000) Greenland Laptev Sea Biogeosciences 18 12 3637 3655 |
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Open Polar |
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Copernicus Publications: E-Journals |
op_collection_id |
ftcopernicus |
language |
English |
description |
Permafrost degradation in the catchment of major Siberian rivers, combined with higher precipitation in a warming climate, could increase the flux of terrestrially derived dissolved organic matter (tDOM) into the Arctic Ocean (AO). Each year, ∼ 7.9 Tg of dissolved organic carbon (DOC) is discharged into the AO via the three largest rivers that flow into the Laptev Sea (LS) and East Siberian Sea (ESS). A significant proportion of this tDOM-rich river water undergoes at least one freeze–melt cycle in the land-fast ice that forms along the coast of the Laptev and East Siberian seas in winter. To better understand how growth and melting of land-fast ice affect dissolved organic matter (DOM) dynamics in the LS and ESS, we determined DOC concentrations and the optical properties of coloured dissolved organic matter (CDOM) in sea ice, river water and seawater. The data set, covering different seasons over a 9-year period (2010–2019), was complemented by oceanographic measurements ( T , S ) and determination of the oxygen isotope composition of the seawater. Although removal of tDOM cannot be ruled out, our study suggests that conservative mixing of high-tDOM river water and sea-ice meltwater with low-tDOM seawater is the major factor controlling the surface distribution of tDOM in the LS and ESS. A case study based on data from winter 2012 and spring 2014 reveals that the mixing of about 273 km 3 of low-tDOM land-fast-ice meltwater (containing ∼ 0.3 Tg DOC) with more than 200 km 3 of high-tDOM Lena River water discharged during the spring freshet ( ∼ 2.8 Tg DOC yr −1 ) plays a dominant role in this respect. The mixing of the two low-salinity surface water masses is possible because the meltwater and the river water of the spring freshet flow into the southeastern LS at the same time every year (May–July). In addition, budget calculations indicate that in the course of the growth of land-fast ice in the southeastern LS, ∼ 1.2 Tg DOC yr −1 ( ± 0.54 Tg) can be expelled from the growing ice in winter, together with brines. These DOC-rich brines can then be transported across the shelves into the Arctic halocline and the Transpolar Drift Current flowing from the Siberian Shelf towards Greenland. The study of dissolved organic matter dynamics in the AO is important not only to decipher the Arctic carbon cycle but also because CDOM regulates physical processes such as radiative forcing in the upper ocean, which has important effects on sea surface temperature, water column stratification, biological productivity and UV penetration. |
format |
Text |
author |
Hölemann, Jens A. Juhls, Bennet Bauch, Dorothea Janout, Markus Koch, Boris P. Heim, Birgit |
spellingShingle |
Hölemann, Jens A. Juhls, Bennet Bauch, Dorothea Janout, Markus Koch, Boris P. Heim, Birgit The impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the Laptev and East Siberian seas (Siberian Arctic) |
author_facet |
Hölemann, Jens A. Juhls, Bennet Bauch, Dorothea Janout, Markus Koch, Boris P. Heim, Birgit |
author_sort |
Hölemann, Jens A. |
title |
The impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the Laptev and East Siberian seas (Siberian Arctic) |
title_short |
The impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the Laptev and East Siberian seas (Siberian Arctic) |
title_full |
The impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the Laptev and East Siberian seas (Siberian Arctic) |
title_fullStr |
The impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the Laptev and East Siberian seas (Siberian Arctic) |
title_full_unstemmed |
The impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the Laptev and East Siberian seas (Siberian Arctic) |
title_sort |
impact of the freeze–melt cycle of land-fast ice on the distribution of dissolved organic matter in the laptev and east siberian seas (siberian arctic) |
publishDate |
2021 |
url |
https://doi.org/10.5194/bg-18-3637-2021 https://bg.copernicus.org/articles/18/3637/2021/ |
long_lat |
ENVELOPE(166.000,166.000,74.000,74.000) |
geographic |
Arctic Arctic Ocean East Siberian Sea Greenland Laptev Sea |
geographic_facet |
Arctic Arctic Ocean East Siberian Sea Greenland Laptev Sea |
genre |
Arctic Arctic Ocean East Siberian Sea Greenland Ice laptev Laptev Sea lena river permafrost Sea ice |
genre_facet |
Arctic Arctic Ocean East Siberian Sea Greenland Ice laptev Laptev Sea lena river permafrost Sea ice |
op_source |
eISSN: 1726-4189 |
op_relation |
doi:10.5194/bg-18-3637-2021 https://bg.copernicus.org/articles/18/3637/2021/ |
op_doi |
https://doi.org/10.5194/bg-18-3637-2021 |
container_title |
Biogeosciences |
container_volume |
18 |
container_issue |
12 |
container_start_page |
3637 |
op_container_end_page |
3655 |
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1766329490775998464 |