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Chlorophyll-a transformations associated with sinking diatoms during termination of a North Atlantic spring bloom

Chlorophyll-a transformations associated with sinking diatoms during termination of a North Atlantic spring bloom
Chlorophyll-a transformations associated with sinking diatoms during termination of a North Atlantic spring bloom
A research cruise in the North Atlantic during the annual diatom bloom provided an ideal platform to study chlorophyll-a (chl-a) transformations associated with a large scale diatom bloom and export below the photic zone. On one deployment, Lagrangian sediment traps captured a significant flux of aggregated diatom cells produced during the termination of the main bloom. We examined the distribution of chl-a transformation products in sinking particles from the sediment traps and in suspended particles from the water column using high-resolution HPLC with multistage mass spectrometry (LC–MSn). There was a dramatic change in the distribution of chl-a and its transformation products between the pre-sinking period, when the average chl-a concentration integrated over the upper 50 m was 68 ± 36 mg m? 2, and the post-sinking period, when it was 30 ± 11 mg m? 2. Before the diatom bloom left the euphotic zone (pre-sinking), suspended particles contained a considerably higher percentage of pheophorbide-a and other chl-a transformation products (27%) than during the post-sinking period (10%). Despite high levels of spatial variability in the chl-a concentration, and despite sampling from both within and outside a main bloom patch, the chl-a transformation products in suspended particles did not exhibit spatial variability. Sinking particles associated with the diatom bloom export had low POC:chl-a ratios (52–97), suggesting undegraded phytoplankton cells. However, the samples with especially low POC:chl-a ratios exhibited similar distributions of chl-a transformation products to those with a higher ratio. The proportions of demetalated and de-esterified transformation products increased with depth of suspended particles, although significant levels of these products were also found in the uppermost 20 m during the bloom. This suggests processes in both surface waters and through the water column led to the formation of these products.
Chlorophyll-a transformation products, Diatom bloom, Bloom termination, Sinking particles, Suspended particles, North Atlantic
0304-4203
23-33
Bale, Nicole J.
708a4765-170b-4593-a7f2-a8d3710b3d89
Airs, Ruth L.
e12cc56f-75bc-48d7-b3fd-3e79475620fe
Martin, Patrick
01ce1c59-3926-46c9-a556-fac39e0ee16b
Lampitt, Richard S.
dfc3785c-fc7d-41fa-89ee-d0c6e27503ad
Llewellyn, Carole A.
16d62d11-8ee4-4ab1-a42d-9fad3ef42dbd
Bale, Nicole J.
708a4765-170b-4593-a7f2-a8d3710b3d89
Airs, Ruth L.
e12cc56f-75bc-48d7-b3fd-3e79475620fe
Martin, Patrick
01ce1c59-3926-46c9-a556-fac39e0ee16b
Lampitt, Richard S.
dfc3785c-fc7d-41fa-89ee-d0c6e27503ad
Llewellyn, Carole A.
16d62d11-8ee4-4ab1-a42d-9fad3ef42dbd

Bale, Nicole J., Airs, Ruth L., Martin, Patrick, Lampitt, Richard S. and Llewellyn, Carole A. (2015) Chlorophyll-a transformations associated with sinking diatoms during termination of a North Atlantic spring bloom. Marine Chemistry, 172, 23-33.

Record type: Article

Abstract

A research cruise in the North Atlantic during the annual diatom bloom provided an ideal platform to study chlorophyll-a (chl-a) transformations associated with a large scale diatom bloom and export below the photic zone. On one deployment, Lagrangian sediment traps captured a significant flux of aggregated diatom cells produced during the termination of the main bloom. We examined the distribution of chl-a transformation products in sinking particles from the sediment traps and in suspended particles from the water column using high-resolution HPLC with multistage mass spectrometry (LC–MSn). There was a dramatic change in the distribution of chl-a and its transformation products between the pre-sinking period, when the average chl-a concentration integrated over the upper 50 m was 68 ± 36 mg m? 2, and the post-sinking period, when it was 30 ± 11 mg m? 2. Before the diatom bloom left the euphotic zone (pre-sinking), suspended particles contained a considerably higher percentage of pheophorbide-a and other chl-a transformation products (27%) than during the post-sinking period (10%). Despite high levels of spatial variability in the chl-a concentration, and despite sampling from both within and outside a main bloom patch, the chl-a transformation products in suspended particles did not exhibit spatial variability. Sinking particles associated with the diatom bloom export had low POC:chl-a ratios (52–97), suggesting undegraded phytoplankton cells. However, the samples with especially low POC:chl-a ratios exhibited similar distributions of chl-a transformation products to those with a higher ratio. The proportions of demetalated and de-esterified transformation products increased with depth of suspended particles, although significant levels of these products were also found in the uppermost 20 m during the bloom. This suggests processes in both surface waters and through the water column led to the formation of these products.

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More information

Published date: 20 May 2015
Keywords: Chlorophyll-a transformation products, Diatom bloom, Bloom termination, Sinking particles, Suspended particles, North Atlantic
Organisations: Ocean and Earth Science, Marine Biogeochemistry

Identifiers

Local EPrints ID: 376931
URI: https://eprints.soton.ac.uk/id/eprint/376931
ISSN: 0304-4203
PURE UUID: ac2523bf-49f4-4acb-8382-4fe53a01f4b8

Catalogue record

Date deposited: 08 May 2015 13:21
Last modified: 30 Sep 2017 21:57

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