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

Bale, Nicole J.; Airs, Ruth L.; Martin, Patrick; Lampitt, Richard S.; Llewellyn, Carole A.. 2015 Chlorophyll-a transformations associated with sinking diatoms during termination of a North Atlantic spring bloom. Marine Chemistry, 172. 23-33. 10.1016/j.marchem.2015.03.005

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Abstract/Summary

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.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/j.marchem.2015.03.005
ISSN: 03044203
Additional Keywords: Chlorophyll-a transformation products; Diatom bloom; Bloom termination; Sinking particles; Suspended particles; North Atlantic
NORA Subject Terms: Marine Sciences
Date made live: 08 May 2015 13:28 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/510761

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