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)

<p>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, <span class="inline-formula">∼&l...

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Main Authors:	J. A. Hölemann, B. Juhls, D. Bauch, M. Janout, B. P. Koch, B. Heim
Format:	Article
Language:	English
Published:	Copernicus Publications 2021-06-01
Series:	Biogeosciences
Online Access:	https://bg.copernicus.org/articles/18/3637/2021/bg-18-3637-2021.pdf

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author	J. A. Hölemann B. Juhls B. Juhls D. Bauch D. Bauch M. Janout B. P. Koch B. P. Koch B. Heim
author_facet	J. A. Hölemann B. Juhls B. Juhls D. Bauch D. Bauch M. Janout B. P. Koch B. P. Koch B. Heim
author_sort	J. A. Hölemann
collection	DOAJ
description	<p>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, <span class="inline-formula">∼</span> 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 (<span class="inline-formula"><i>T</i></span>, <span class="inline-formula"><i>S</i></span>) and determination of the oxygen isotope composition of the seawater.</p> <p>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<span class="inline-formula"><sup>3</sup></span> of low-tDOM land-fast-ice meltwater (containing <span class="inline-formula">∼</span> 0.3 Tg DOC) with more than 200 km<span class="inline-formula"><sup>3</sup></span> of high-tDOM Lena River water discharged during the spring freshet (<span class="inline-formula">∼</span> 2.8 Tg DOC yr<span class="inline-formula"><sup>−1</sup></span>) 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, <span class="inline-formula">∼</span> 1.2 Tg DOC yr<span class="inline-formula"><sup>−1</sup></span> (<span class="inline-formula">±</span> 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.</p> <p>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.</p>
first_indexed	2024-12-14T22:53:25Z
format	Article
id	doaj.art-3441c10fe42a4a4bb02f231346d85178
institution	Directory Open Access Journal
issn	1726-4170 1726-4189
language	English
last_indexed	2024-12-14T22:53:25Z
publishDate	2021-06-01
publisher	Copernicus Publications
record_format	Article
series	Biogeosciences
spelling	doaj.art-3441c10fe42a4a4bb02f231346d851782022-12-21T22:44:39ZengCopernicus PublicationsBiogeosciences1726-41701726-41892021-06-01183637365510.5194/bg-18-3637-2021The 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)J. A. Hölemann0B. Juhls1B. Juhls2D. Bauch3D. Bauch4M. Janout5B. P. Koch6B. P. Koch7B. Heim8Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, GermanyDepartment of Earth Sciences, Institute for Space Sciences, Freie Universität Berlin, Berlin, GermanyAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, GermanyLeibniz Laboratory for Radiometric Dating and Stable Isotope Research, University of Kiel CAU, Kiel, GermanyGEOMAR, Helmholtz Centre for Ocean Research, Kiel, GermanyAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, GermanyAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, GermanyFaculty 1, University of Applied Sciences Bremerhaven, Bremerhaven, GermanyAlfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany<p>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, <span class="inline-formula">∼</span> 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 (<span class="inline-formula"><i>T</i></span>, <span class="inline-formula"><i>S</i></span>) and determination of the oxygen isotope composition of the seawater.</p> <p>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<span class="inline-formula"><sup>3</sup></span> of low-tDOM land-fast-ice meltwater (containing <span class="inline-formula">∼</span> 0.3 Tg DOC) with more than 200 km<span class="inline-formula"><sup>3</sup></span> of high-tDOM Lena River water discharged during the spring freshet (<span class="inline-formula">∼</span> 2.8 Tg DOC yr<span class="inline-formula"><sup>−1</sup></span>) 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, <span class="inline-formula">∼</span> 1.2 Tg DOC yr<span class="inline-formula"><sup>−1</sup></span> (<span class="inline-formula">±</span> 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.</p> <p>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.</p>https://bg.copernicus.org/articles/18/3637/2021/bg-18-3637-2021.pdf
spellingShingle	J. A. Hölemann B. Juhls B. Juhls D. Bauch D. Bauch M. Janout B. P. Koch B. P. Koch B. Heim 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) Biogeosciences
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_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_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_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
url	https://bg.copernicus.org/articles/18/3637/2021/bg-18-3637-2021.pdf
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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)

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