TY - JOUR
T1 - Primary production dynamics on the Agulhas Bank in autumn
AU - Poulton, Alex J.
AU - Mazwane, Sixolile L.
AU - Godfrey, Brian
AU - Carvalho, Filipa
AU - Mawji, Edward
AU - Wihsgott, Julianne U.
AU - Noyon, Margaux
N1 - Funding Information:
We thank the captain and crew of the RV Ellen Khuzwayo, as well as the Department of Agriculture, Forestry and Fisheries (now DFFE). We are also thankful to the scientists of the SOLSTICE-WIO project for fruitful discussions. This publication was produced with the financial support of the Global Challenges Research Fund (GCRF), UK , in the framework of the SOLSTICE-WIO project, NE/P021050/1 . This work was supported by the UK-SA Bilateral Chair of Ocean Science and Marine Food Security funded by the NRF/DST Grant ( 98399 ) and Newton Funds.
Funding Information:
We thank the captain and crew of the RV Ellen Khuzwayo, as well as the Department of Agriculture, Forestry and Fisheries (now DFFE). We are also thankful to the scientists of the SOLSTICE-WIO project for fruitful discussions. This publication was produced with the financial support of the Global Challenges Research Fund (GCRF), UK, in the framework of the SOLSTICE-WIO project, NE/P021050/1. This work was supported by the UK-SA Bilateral Chair of Ocean Science and Marine Food Security funded by the NRF/DST Grant (98399) and Newton Funds.
Publisher Copyright:
© 2022 The Authors
PY - 2022/9
Y1 - 2022/9
N2 - The Agulhas Bank is a productive shelf sea, supporting important fish stocks, nursery grounds, and spawning sites. Few studies have examined the dynamics of primary production and the physio-chemical conditions that support this productivity during autumn. We report from a 14-day, 51-station survey of the central and eastern (21-27°E) Agulhas Bank in March 2019, during which we examined water-column structure, macronutrients, chlorophyll-a (total and size-fractionated), diatom cell counts and Net Primary Production (NPP). East to west trends were observed, with surface mixed layers (SML) and stratification increasing to the west. Euphotic zones were deeper than the SML, with SML irradiance conditions indicative of favorable light conditions for NPP. On average, surface waters contained ∼1.2 μmol N L−1 of nitrate (nitrate + nitrite; NO3) and ∼3 μmol Si L−1 of silicic acid, which contrasts with nutrient deficient subtropical source waters. Surface chlorophyll-a ranged from 0.3 to 5.1 mg m−3, with high values inshore and near the shelf break. Nanoplankton (2–20 μm) dominated size-fractionated chlorophyll-a, with microplankton contributions increasing to the west. Measurements of NPP were collected at seven stations, ranging from 0.3 to 1.1 g C m−2 d−1, with a statistically significant relationship between integrated NPP and surface chlorophyll-a allowing further estimates of NPP (0.1–1.1 g C m−2 d−1). We estimated nitrogen-demand to support NPP, with a comparison to surface NO3 indicating ample nutrients to support daily NPP. Around half of the stations possessed a Subsurface Chlorophyll Maximum (SCM), with chlorophyll-a ranging from 1.7 to 10.3 mg m−3. Characteristics of the SCM (depth, light level, chlorophyll-to-carbon ratios) showed east to west variability, implying that the mechanisms of SCM formation ranged from in-situ growth (east) to photo-acclimation (west).
AB - The Agulhas Bank is a productive shelf sea, supporting important fish stocks, nursery grounds, and spawning sites. Few studies have examined the dynamics of primary production and the physio-chemical conditions that support this productivity during autumn. We report from a 14-day, 51-station survey of the central and eastern (21-27°E) Agulhas Bank in March 2019, during which we examined water-column structure, macronutrients, chlorophyll-a (total and size-fractionated), diatom cell counts and Net Primary Production (NPP). East to west trends were observed, with surface mixed layers (SML) and stratification increasing to the west. Euphotic zones were deeper than the SML, with SML irradiance conditions indicative of favorable light conditions for NPP. On average, surface waters contained ∼1.2 μmol N L−1 of nitrate (nitrate + nitrite; NO3) and ∼3 μmol Si L−1 of silicic acid, which contrasts with nutrient deficient subtropical source waters. Surface chlorophyll-a ranged from 0.3 to 5.1 mg m−3, with high values inshore and near the shelf break. Nanoplankton (2–20 μm) dominated size-fractionated chlorophyll-a, with microplankton contributions increasing to the west. Measurements of NPP were collected at seven stations, ranging from 0.3 to 1.1 g C m−2 d−1, with a statistically significant relationship between integrated NPP and surface chlorophyll-a allowing further estimates of NPP (0.1–1.1 g C m−2 d−1). We estimated nitrogen-demand to support NPP, with a comparison to surface NO3 indicating ample nutrients to support daily NPP. Around half of the stations possessed a Subsurface Chlorophyll Maximum (SCM), with chlorophyll-a ranging from 1.7 to 10.3 mg m−3. Characteristics of the SCM (depth, light level, chlorophyll-to-carbon ratios) showed east to west variability, implying that the mechanisms of SCM formation ranged from in-situ growth (east) to photo-acclimation (west).
KW - Phytoplankton
KW - Shelf sea
KW - Upwelling
KW - Western boundary current
UR - http://www.scopus.com/inward/record.url?scp=85135799872&partnerID=8YFLogxK
U2 - 10.1016/j.dsr2.2022.105153
DO - 10.1016/j.dsr2.2022.105153
M3 - Article
SN - 0967-0645
VL - 203
JO - Deep-Sea Research Part II: Topical Studies in Oceanography
JF - Deep-Sea Research Part II: Topical Studies in Oceanography
M1 - 105153
ER -