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Capturing optically important constituents and properties in a marine biogeochemical and ecosystem model

Capturing optically important constituents and properties in a marine biogeochemical and ecosystem model
Capturing optically important constituents and properties in a marine biogeochemical and ecosystem model
We present a numerical model of the ocean that couples a three-stream radiative transfer component with a marine biogeochemical–ecosystem component in a dynamic three-dimensional physical framework. The radiative transfer component resolves the penetration of spectral irradiance as it is absorbed and scattered within the water column. We explicitly include the effect of several optically important water constituents (different phytoplankton functional types; detrital particles; and coloured dissolved organic matter, CDOM). The model is evaluated against in situ-observed and satellite-derived products. In particular we compare to concurrently measured biogeochemical, ecosystem, and optical data along a meridional transect of the Atlantic Ocean. The simulation captures the patterns and magnitudes of these data, and estimates surface upwelling irradiance analogous to that observed by ocean colour satellite instruments. We find that incorporating the different optically important constituents explicitly and including spectral irradiance was crucial to capture the variability in the depth of the subsurface chlorophyll a (Chl a) maximum. We conduct a series of sensitivity experiments to demonstrate, globally, the relative importance of each of the water constituents, as well as the crucial feedbacks between the light field, the relative fitness of phytoplankton types, and the biogeochemistry of the ocean. CDOM has proportionally more importance at attenuating light at short wavelengths and in more productive waters, phytoplankton absorption is relatively more important at the subsurface Chl a maximum, and water molecules have the greatest contribution when concentrations of other constituents are low, such as in the oligotrophic gyres. Scattering had less effect on attenuation, but since it is important for the amount and type of upwelling irradiance, it is crucial for setting sea surface reflectance. Strikingly, sensitivity experiments in which absorption by any of the optical constituents was increased led to a decrease in the size of the oligotrophic regions of the subtropical gyres: lateral nutrient supplies were enhanced as a result of decreasing high-latitude productivity. This new model that captures bio-optical feedbacks will be important for improving our understanding of the role of light and optical constituents on ocean biogeochemistry, especially in a changing environment. Further, resolving surface upwelling irradiance will make it easier to connect to satellite-derived products in the future.
1726-4170
4447-4481
Dutkiewicz, S.
a2255d47-6686-47a1-bdee-5696ffa331c3
Hickman, A.E.
a99786c6-65e6-48c8-8b58-0d3b5608be92
Jahn, O.
a9d6758c-c0a0-45d4-ac90-1b6726957fe5
Gregg, W.W.
c0f328c3-5817-4c9c-95f5-bee0cf8fa2f2
Mouw, C.B.
78f2e529-3e91-4395-ae49-b29d885f5045
Follows, M.J.
b2eaa10d-93af-421a-a37a-5a1e446360b3
Dutkiewicz, S.
a2255d47-6686-47a1-bdee-5696ffa331c3
Hickman, A.E.
a99786c6-65e6-48c8-8b58-0d3b5608be92
Jahn, O.
a9d6758c-c0a0-45d4-ac90-1b6726957fe5
Gregg, W.W.
c0f328c3-5817-4c9c-95f5-bee0cf8fa2f2
Mouw, C.B.
78f2e529-3e91-4395-ae49-b29d885f5045
Follows, M.J.
b2eaa10d-93af-421a-a37a-5a1e446360b3

Dutkiewicz, S., Hickman, A.E., Jahn, O., Gregg, W.W., Mouw, C.B. and Follows, M.J. (2015) Capturing optically important constituents and properties in a marine biogeochemical and ecosystem model. Biogeosciences, 12 (14), 4447-4481. (doi:10.5194/bg-12-4447-2015).

Record type: Article

Abstract

We present a numerical model of the ocean that couples a three-stream radiative transfer component with a marine biogeochemical–ecosystem component in a dynamic three-dimensional physical framework. The radiative transfer component resolves the penetration of spectral irradiance as it is absorbed and scattered within the water column. We explicitly include the effect of several optically important water constituents (different phytoplankton functional types; detrital particles; and coloured dissolved organic matter, CDOM). The model is evaluated against in situ-observed and satellite-derived products. In particular we compare to concurrently measured biogeochemical, ecosystem, and optical data along a meridional transect of the Atlantic Ocean. The simulation captures the patterns and magnitudes of these data, and estimates surface upwelling irradiance analogous to that observed by ocean colour satellite instruments. We find that incorporating the different optically important constituents explicitly and including spectral irradiance was crucial to capture the variability in the depth of the subsurface chlorophyll a (Chl a) maximum. We conduct a series of sensitivity experiments to demonstrate, globally, the relative importance of each of the water constituents, as well as the crucial feedbacks between the light field, the relative fitness of phytoplankton types, and the biogeochemistry of the ocean. CDOM has proportionally more importance at attenuating light at short wavelengths and in more productive waters, phytoplankton absorption is relatively more important at the subsurface Chl a maximum, and water molecules have the greatest contribution when concentrations of other constituents are low, such as in the oligotrophic gyres. Scattering had less effect on attenuation, but since it is important for the amount and type of upwelling irradiance, it is crucial for setting sea surface reflectance. Strikingly, sensitivity experiments in which absorption by any of the optical constituents was increased led to a decrease in the size of the oligotrophic regions of the subtropical gyres: lateral nutrient supplies were enhanced as a result of decreasing high-latitude productivity. This new model that captures bio-optical feedbacks will be important for improving our understanding of the role of light and optical constituents on ocean biogeochemistry, especially in a changing environment. Further, resolving surface upwelling irradiance will make it easier to connect to satellite-derived products in the future.

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Accepted/In Press date: 4 July 2015
e-pub ahead of print date: 29 July 2015
Published date: 29 July 2015
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 382584
URI: http://eprints.soton.ac.uk/id/eprint/382584
ISSN: 1726-4170
PURE UUID: 381aa34b-55e9-476a-841d-d4e9023df060
ORCID for A.E. Hickman: ORCID iD orcid.org/0000-0002-2774-3934

Catalogue record

Date deposited: 07 Oct 2015 09:35
Last modified: 26 Nov 2021 02:58

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Contributors

Author: S. Dutkiewicz
Author: A.E. Hickman ORCID iD
Author: O. Jahn
Author: W.W. Gregg
Author: C.B. Mouw
Author: M.J. Follows

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