Early spring phytoplankton dynamics in the subpolar North Atlantic: The influence of heterotrohic-protist herbivory
To assess the importance of herbivory by heterotrophic protists in relation to mixed-layer depth prior to the spring phytoplankton bloom, we measured phytoplankton growth and heterotrophic-protist grazing rates during the March/April 2012 EuroBasin Deep Convection cruise in the subpolar North Atlant...
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ftunivrhodeislan:oai:digitalcommons.uri.edu:dissertations-3211 2023-05-15T17:32:08+02:00 Early spring phytoplankton dynamics in the subpolar North Atlantic: The influence of heterotrohic-protist herbivory Morison, Francoise 2014-01-01T08:00:00Z https://digitalcommons.uri.edu/dissertations/AAI1560319 ENG eng DigitalCommons@URI https://digitalcommons.uri.edu/dissertations/AAI1560319 Dissertations and Master's Theses (Campus Access) Biological oceanography text 2014 ftunivrhodeislan 2021-06-29T19:21:17Z To assess the importance of herbivory by heterotrophic protists in relation to mixed-layer depth prior to the spring phytoplankton bloom, we measured phytoplankton growth and heterotrophic-protist grazing rates during the March/April 2012 EuroBasin Deep Convection cruise in the subpolar North Atlantic. We performed 15 dilution experiments during 2-4 visits at one shelf (160 m) and two deep (~1300 m) stations. Of the two deep stations, one had a mean mixed-layer depth of 476 m, whereas the other was stratified (46 m). Euphotic depth averaged ~70 m at both stations. Initial chlorophyll-a varied from 0.2 to 1.9 μg L-1 at the deep mixed layer station and from 0.5 to 1.0 μg L-1 at the stratified station. In 80 % of the experiments, growth rates exceeded grazing mortality rates, regardless of mixed layer depth. Large mixed layer depth coincided with phytoplankton growth and grazing mortality rates that varied over a similar range from 0 to 0.6 d-1, and to an average grazing-impact representing 50% of primary production (PP). At the stratified station, phytoplankton growth rates varied from 0.18 to 0.41 d-1, grazing mortality rates varied from 0.11 to 0.34 d-1, and a temporal shift from a positive to a negative balance between growth and grazing rates caused the proportion of PP consumed to increase from 60% to 180%. Variations in in situ chlorophyll-a could not be explained where the mixed layer was deep, whereas at the stratified station the balance between rate estimates of phytoplankton growth and grazing mortality rates explained 98 % of measured changes in chlorophyll-a. These results suggest a difference in the dominant surface loss process at the two stations: grazing at the stratified station vs. potential sinking aided by vertical mixing where mixed layer was deep. Text North Atlantic University of Rhode Island: DigitalCommons@URI |
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Open Polar |
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University of Rhode Island: DigitalCommons@URI |
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ftunivrhodeislan |
language |
English |
topic |
Biological oceanography |
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Biological oceanography Morison, Francoise Early spring phytoplankton dynamics in the subpolar North Atlantic: The influence of heterotrohic-protist herbivory |
topic_facet |
Biological oceanography |
description |
To assess the importance of herbivory by heterotrophic protists in relation to mixed-layer depth prior to the spring phytoplankton bloom, we measured phytoplankton growth and heterotrophic-protist grazing rates during the March/April 2012 EuroBasin Deep Convection cruise in the subpolar North Atlantic. We performed 15 dilution experiments during 2-4 visits at one shelf (160 m) and two deep (~1300 m) stations. Of the two deep stations, one had a mean mixed-layer depth of 476 m, whereas the other was stratified (46 m). Euphotic depth averaged ~70 m at both stations. Initial chlorophyll-a varied from 0.2 to 1.9 μg L-1 at the deep mixed layer station and from 0.5 to 1.0 μg L-1 at the stratified station. In 80 % of the experiments, growth rates exceeded grazing mortality rates, regardless of mixed layer depth. Large mixed layer depth coincided with phytoplankton growth and grazing mortality rates that varied over a similar range from 0 to 0.6 d-1, and to an average grazing-impact representing 50% of primary production (PP). At the stratified station, phytoplankton growth rates varied from 0.18 to 0.41 d-1, grazing mortality rates varied from 0.11 to 0.34 d-1, and a temporal shift from a positive to a negative balance between growth and grazing rates caused the proportion of PP consumed to increase from 60% to 180%. Variations in in situ chlorophyll-a could not be explained where the mixed layer was deep, whereas at the stratified station the balance between rate estimates of phytoplankton growth and grazing mortality rates explained 98 % of measured changes in chlorophyll-a. These results suggest a difference in the dominant surface loss process at the two stations: grazing at the stratified station vs. potential sinking aided by vertical mixing where mixed layer was deep. |
format |
Text |
author |
Morison, Francoise |
author_facet |
Morison, Francoise |
author_sort |
Morison, Francoise |
title |
Early spring phytoplankton dynamics in the subpolar North Atlantic: The influence of heterotrohic-protist herbivory |
title_short |
Early spring phytoplankton dynamics in the subpolar North Atlantic: The influence of heterotrohic-protist herbivory |
title_full |
Early spring phytoplankton dynamics in the subpolar North Atlantic: The influence of heterotrohic-protist herbivory |
title_fullStr |
Early spring phytoplankton dynamics in the subpolar North Atlantic: The influence of heterotrohic-protist herbivory |
title_full_unstemmed |
Early spring phytoplankton dynamics in the subpolar North Atlantic: The influence of heterotrohic-protist herbivory |
title_sort |
early spring phytoplankton dynamics in the subpolar north atlantic: the influence of heterotrohic-protist herbivory |
publisher |
DigitalCommons@URI |
publishDate |
2014 |
url |
https://digitalcommons.uri.edu/dissertations/AAI1560319 |
genre |
North Atlantic |
genre_facet |
North Atlantic |
op_source |
Dissertations and Master's Theses (Campus Access) |
op_relation |
https://digitalcommons.uri.edu/dissertations/AAI1560319 |
_version_ |
1766130081548206080 |