Estimating the seasonal impact of optically significant water constituents on surface heating rates in the western Baltic Sea
<p>Heating rates induced by optically significant water constituents (OSCs), e.g. phytoplankton and coloured dissolved organic matter (CDOM), contribute to the seasonal modulation of thermal energy fluxes across the ocean–atmosphere interface in coastal and regional shelf seas. This is investi...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2023-07-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/20/2743/2023/bg-20-2743-2023.pdf |
| _version_ | 1797780981378187264 |
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| author | B. E. Cahill B. E. Cahill P. Kowalczuk L. Kritten U. Gräwe J. Wilkin J. Fischer |
| author_facet | B. E. Cahill B. E. Cahill P. Kowalczuk L. Kritten U. Gräwe J. Wilkin J. Fischer |
| author_sort | B. E. Cahill |
| collection | DOAJ |
| description | <p>Heating rates induced by optically significant water constituents
(OSCs), e.g. phytoplankton and coloured dissolved organic matter (CDOM),
contribute to the seasonal modulation of thermal energy fluxes across the
ocean–atmosphere interface in coastal and regional shelf seas. This is
investigated in the western Baltic Sea, a marginal sea characterised by
considerable inputs of freshwater carrying nutrients and CDOM and by complex
bio-optical and hydrodynamic processes. Using a coupled bio-optical ocean
model (ROMS–Bio-Optic), the inherent optical properties of different OSCs
are modelled under varying environmental conditions, and the underwater light
field is spectrally resolved in a dynamic ocean. We estimate the relative
contribution of these OSCs to the divergence of the heat flux and heating
rates and find that, while phytoplankton and CDOM both contribute to surface
heating in summer, phytoplankton dominates the OSC contribution to heating
in spring, and CDOM dominates the OSC contribution to heating in autumn. The
study shows that seasonal and spatial changes in OSCs in the western Baltic
Sea have a small but noticeable impact on radiative heating in surface
waters and consequences for the exchange of energy fluxes across the air–sea
interface and the distribution of heat within the water column. In the
Pomeranian Bight, where riverine influx of CDOM is strongest, water-constituent-induced heating rates in surface waters in 2018 are estimated to
be between 0.8 and 0.9 K m<span class="inline-formula"><sup>−1</sup></span> d<span class="inline-formula"><sup>−1</sup></span> in spring and summer,
predominantly as a result of increased absorption by phytoplankton and CDOM.
Further offshore, OSC-induced heating rates during the same periods are
estimated to be between 0.4 and 0.8 K m<span class="inline-formula"><sup>−1</sup></span> d<span class="inline-formula"><sup>−1</sup></span>. Warmer surface
waters are balanced by cooler subsurface waters. Surface heat fluxes
(latent, sensible and longwave) respond to warmer sea surface temperatures,
with a small increase in heat loss to the atmosphere of 5 W m<span class="inline-formula"><sup>−2</sup></span> during
the period April to September. We find relatively good agreement between our
modelled water constituent absorption and in situ and satellite
observations. More rigorous co-located heating-rate calculations using an
atmosphere–ocean radiative transfer model provide evidence of the
suitability of the ROMS–Bio-Optic model for estimating heating rates.</p> |
| first_indexed | 2024-03-12T23:51:27Z |
| format | Article |
| id | doaj.art-9e83d63862af49b58b60bf8f795efe8c |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-03-12T23:51:27Z |
| publishDate | 2023-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-9e83d63862af49b58b60bf8f795efe8c2023-07-13T13:40:14ZengCopernicus PublicationsBiogeosciences1726-41701726-41892023-07-01202743276810.5194/bg-20-2743-2023Estimating the seasonal impact of optically significant water constituents on surface heating rates in the western Baltic SeaB. E. Cahill0B. E. Cahill1P. Kowalczuk2L. Kritten3U. Gräwe4J. Wilkin5J. Fischer6Physical Oceanography and Instrumentation, Leibniz Institute for Baltic Sea Research, Warnemünde 18119, GermanyInstitute of Meteorology, Free University Berlin, Berlin 12165, GermanyInstitute of Oceanology PAS, Powstańców Warszawy 55, 81-712 Sopot, PolandInstitute of Meteorology, Free University Berlin, Berlin 12165, GermanyPhysical Oceanography and Instrumentation, Leibniz Institute for Baltic Sea Research, Warnemünde 18119, GermanyDepartment of Marine and Coastal Sciences, Rutgers University, New Brunswick, 08901 NJ, USAInstitute of Meteorology, Free University Berlin, Berlin 12165, Germany<p>Heating rates induced by optically significant water constituents (OSCs), e.g. phytoplankton and coloured dissolved organic matter (CDOM), contribute to the seasonal modulation of thermal energy fluxes across the ocean–atmosphere interface in coastal and regional shelf seas. This is investigated in the western Baltic Sea, a marginal sea characterised by considerable inputs of freshwater carrying nutrients and CDOM and by complex bio-optical and hydrodynamic processes. Using a coupled bio-optical ocean model (ROMS–Bio-Optic), the inherent optical properties of different OSCs are modelled under varying environmental conditions, and the underwater light field is spectrally resolved in a dynamic ocean. We estimate the relative contribution of these OSCs to the divergence of the heat flux and heating rates and find that, while phytoplankton and CDOM both contribute to surface heating in summer, phytoplankton dominates the OSC contribution to heating in spring, and CDOM dominates the OSC contribution to heating in autumn. The study shows that seasonal and spatial changes in OSCs in the western Baltic Sea have a small but noticeable impact on radiative heating in surface waters and consequences for the exchange of energy fluxes across the air–sea interface and the distribution of heat within the water column. In the Pomeranian Bight, where riverine influx of CDOM is strongest, water-constituent-induced heating rates in surface waters in 2018 are estimated to be between 0.8 and 0.9 K m<span class="inline-formula"><sup>−1</sup></span> d<span class="inline-formula"><sup>−1</sup></span> in spring and summer, predominantly as a result of increased absorption by phytoplankton and CDOM. Further offshore, OSC-induced heating rates during the same periods are estimated to be between 0.4 and 0.8 K m<span class="inline-formula"><sup>−1</sup></span> d<span class="inline-formula"><sup>−1</sup></span>. Warmer surface waters are balanced by cooler subsurface waters. Surface heat fluxes (latent, sensible and longwave) respond to warmer sea surface temperatures, with a small increase in heat loss to the atmosphere of 5 W m<span class="inline-formula"><sup>−2</sup></span> during the period April to September. We find relatively good agreement between our modelled water constituent absorption and in situ and satellite observations. More rigorous co-located heating-rate calculations using an atmosphere–ocean radiative transfer model provide evidence of the suitability of the ROMS–Bio-Optic model for estimating heating rates.</p>https://bg.copernicus.org/articles/20/2743/2023/bg-20-2743-2023.pdf |
| spellingShingle | B. E. Cahill B. E. Cahill P. Kowalczuk L. Kritten U. Gräwe J. Wilkin J. Fischer Estimating the seasonal impact of optically significant water constituents on surface heating rates in the western Baltic Sea Biogeosciences |
| title | Estimating the seasonal impact of optically significant water constituents on surface heating rates in the western Baltic Sea |
| title_full | Estimating the seasonal impact of optically significant water constituents on surface heating rates in the western Baltic Sea |
| title_fullStr | Estimating the seasonal impact of optically significant water constituents on surface heating rates in the western Baltic Sea |
| title_full_unstemmed | Estimating the seasonal impact of optically significant water constituents on surface heating rates in the western Baltic Sea |
| title_short | Estimating the seasonal impact of optically significant water constituents on surface heating rates in the western Baltic Sea |
| title_sort | estimating the seasonal impact of optically significant water constituents on surface heating rates in the western baltic sea |
| url | https://bg.copernicus.org/articles/20/2743/2023/bg-20-2743-2023.pdf |
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