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Seasonal and spatial variability in the optical characteristics of DOM in a temperate shelf sea

Seasonal and spatial variability in the optical characteristics of DOM in a temperate shelf sea
Seasonal and spatial variability in the optical characteristics of DOM in a temperate shelf sea

The Celtic Sea is a productive temperate sea located on the Northwest European Shelf. It is an important pathway for the delivery of land-derived material to the North Atlantic Ocean, including dissolved organic matter (DOM). The aim of this study was to determine the seasonal and spatial variability in the magnitude, source and composition of DOM at three sites representing on shelf, central shelf and shelf edge regions in the Celtic Sea, using observations collected during the UK Shelf Sea Biogeochemistry (SSB) research programme (November 2014 - August 2015). The concentration of dissolved organic carbon (DOC) alongside DOM absorbance and fluorescence indices were measured and fluorescence Excitation and Emission Matrices (EEMs) combined with Parallel Factor Analysis (PARAFAC) were used to assess DOM composition and lability. The PARAFAC model identified four unique fluorescent components for autumn (November 2014), winter (March 2015), spring (April 2015) and summer (July 2015) consisting of two humic-like components attributed to terrestrial (C1) and marine sources (C2), and two protein components identified as tyrosine-like (C3) and tryptophan-like (C4) attributed to in situ production. DOC varied seasonally and there were strong cross shelf trends. The protein components (C3 and C4) exhibited large seasonal and within season variability particularly during productive periods. In contrast, there were persistent cross shelf gradients in the CDOM absorption coefficient at 305 nm (a305), the UV specific absorbance at 280 nm (SUVA280), the humification index (HIX), and the humic-like fluorescent components (C1 and C2), which were higher in the on shelf region and decreased towards the shelf edge. The humic-like components and the slope ratio (SR) were significantly correlated with salinity throughout all seasons, indicating a strong influence of terrestrially-derived organic matter in the Celtic Sea, with potentially up to 35% of DOC in the central shelf during winter originating from terrestrial inputs. Results from this study illustrate the importance of monitoring DOM quantitatively and qualitatively for a better understanding of the supply, production, cycling and export of this dynamic organic carbon pool in shelf seas.

Absorbance, DOM, EEMs, Fluorescence, PARAFAC
0079-6611
Carr, Nealy
946bac0c-259f-4fc3-adae-56363ce615ea
Davis, Clare E.
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Blackbird, Sabena
7d07eab9-5745-4697-920e-de1ea0e972c0
Daniels, Lucie R.
859a0d0d-fccc-458d-b218-b1462282d0cd
Preece, Calum
2a81c97b-ef51-4106-a419-c3f0f3b20b29
Woodward, Malcolm
e90435b9-a070-40a0-a2ef-89b35a7b7541
Mahaffey, Claire
6c868a01-2c9b-48b0-ae08-9ecf6b870032
Carr, Nealy
946bac0c-259f-4fc3-adae-56363ce615ea
Davis, Clare E.
65fc2085-7fe4-4af4-b4de-32c06d98c8e7
Blackbird, Sabena
7d07eab9-5745-4697-920e-de1ea0e972c0
Daniels, Lucie R.
859a0d0d-fccc-458d-b218-b1462282d0cd
Preece, Calum
2a81c97b-ef51-4106-a419-c3f0f3b20b29
Woodward, Malcolm
e90435b9-a070-40a0-a2ef-89b35a7b7541
Mahaffey, Claire
6c868a01-2c9b-48b0-ae08-9ecf6b870032

Carr, Nealy, Davis, Clare E., Blackbird, Sabena, Daniels, Lucie R., Preece, Calum, Woodward, Malcolm and Mahaffey, Claire (2018) Seasonal and spatial variability in the optical characteristics of DOM in a temperate shelf sea. Progress in Oceanography. (doi:10.1016/j.pocean.2018.02.025).

Record type: Article

Abstract

The Celtic Sea is a productive temperate sea located on the Northwest European Shelf. It is an important pathway for the delivery of land-derived material to the North Atlantic Ocean, including dissolved organic matter (DOM). The aim of this study was to determine the seasonal and spatial variability in the magnitude, source and composition of DOM at three sites representing on shelf, central shelf and shelf edge regions in the Celtic Sea, using observations collected during the UK Shelf Sea Biogeochemistry (SSB) research programme (November 2014 - August 2015). The concentration of dissolved organic carbon (DOC) alongside DOM absorbance and fluorescence indices were measured and fluorescence Excitation and Emission Matrices (EEMs) combined with Parallel Factor Analysis (PARAFAC) were used to assess DOM composition and lability. The PARAFAC model identified four unique fluorescent components for autumn (November 2014), winter (March 2015), spring (April 2015) and summer (July 2015) consisting of two humic-like components attributed to terrestrial (C1) and marine sources (C2), and two protein components identified as tyrosine-like (C3) and tryptophan-like (C4) attributed to in situ production. DOC varied seasonally and there were strong cross shelf trends. The protein components (C3 and C4) exhibited large seasonal and within season variability particularly during productive periods. In contrast, there were persistent cross shelf gradients in the CDOM absorption coefficient at 305 nm (a305), the UV specific absorbance at 280 nm (SUVA280), the humification index (HIX), and the humic-like fluorescent components (C1 and C2), which were higher in the on shelf region and decreased towards the shelf edge. The humic-like components and the slope ratio (SR) were significantly correlated with salinity throughout all seasons, indicating a strong influence of terrestrially-derived organic matter in the Celtic Sea, with potentially up to 35% of DOC in the central shelf during winter originating from terrestrial inputs. Results from this study illustrate the importance of monitoring DOM quantitatively and qualitatively for a better understanding of the supply, production, cycling and export of this dynamic organic carbon pool in shelf seas.

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Accepted/In Press date: 2018
e-pub ahead of print date: 28 February 2018
Keywords: Absorbance, DOM, EEMs, Fluorescence, PARAFAC

Identifiers

Local EPrints ID: 418722
URI: http://eprints.soton.ac.uk/id/eprint/418722
ISSN: 0079-6611
PURE UUID: 902a2f5c-f897-4333-9b1e-5c8032f06267

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Date deposited: 20 Mar 2018 17:30
Last modified: 16 Dec 2019 18:21

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