About Pigmented Nanoflagellates and the Importance of Mixotrophy in a Coastal Upwelling System

Abstract. Satellite-derived chlorophyll a data using the standard NASA-OC3 (ocean colour) algorithm are strongly biased by coloured dissolved organic matter and suspended sediment of river discharges, which is a particular problem for the western Tasmanian shelf. This work reconstructs phytoplankton blooms in the study region using a quadratic regression between OC3 data and chlorophyll fluorescence based on the fluorescence line height (FLH) data. This regression is derived from satellite data of the nearby Bonney upwelling region, which is devoid of river influences. To this end, analyses of 10 years of MODIS-aqua satellite data reveal the existence of a highly productive ecosystem on the western Tasmanian shelf. The region normally experiences two phytoplankton blooms per annum. The first bloom occurs during late austral summer months as a consequence of upwelling-favourable coastal winds. Hence, the western Tasmanian shelf forms a previously unknown upwelling centre of the regional upwelling system, known as Great South Australian Coastal Upwelling System. The second phytoplankton bloom is a classical spring bloom also developing in the adjacent Tasman Sea. The author postulates that this region forms another important biological hot spot for the regional marine ecosystem.

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Diatoms as a paleoproductivity proxy in the NW Iberian coastal upwelling system (NE Atlantic)

Biogeosciences ◽

10.5194/bg-14-1165-2017 ◽

2017 ◽

Vol 14 (5) ◽

pp. 1165-1179 ◽

Cited By ~ 8

Author(s):

Diana Zúñiga ◽

Celia Santos ◽

María Froján ◽

Emilia Salgueiro ◽

Marta M. Rufino ◽

...

Keyword(s):

Water Column ◽

Surface Sediment ◽

Sediment Trap ◽

Coastal Upwelling ◽

Late Summer ◽

Early Summer ◽

Marine Diatom ◽

Photic Zone ◽

Upwelling System ◽

Water Column Stratification

Abstract. The objective of the current work is to improve our understanding of how water column diatom's abundance and assemblage composition is seasonally transferred from the photic zone to seafloor sediments. To address this, we used a dataset derived from water column, sediment trap and surface sediment samples recovered in the NW Iberian coastal upwelling system. Diatom fluxes (2.2 (±5.6) 106 valves m−2 d−1) represented the majority of the siliceous microorganisms sinking out from the photic zone during all studied years and showed seasonal variability. Contrasting results between water column and sediment trap diatom abundances were found during downwelling periods, as shown by the unexpectedly high diatom export signals when diatom-derived primary production achieved their minimum levels. They were principally related to surface sediment remobilization and intense Minho and Douro river discharge that constitute an additional source of particulate matter to the inner continental shelf. In fact, contributions of allochthonous particles to the sinking material were confirmed by the significant increase of both benthic and freshwater diatoms in the sediment trap assemblage. In contrast, we found that most of the living diatom species blooming during highly productive upwelling periods were dissolved during sinking, and only those resistant to dissolution and the Chaetoceros and Leptocylindrus spp. resting spores were susceptible to being exported and buried. Furthermore, Chaetoceros spp. dominate during spring–early summer, when persistent northerly winds lead to the upwelling of nutrient-rich waters on the shelf, while Leptocylindrus spp. appear associated with late-summer upwelling relaxation, characterized by water column stratification and nutrient depletion. These findings evidence that the contributions of these diatom genera to the sediment's total marine diatom assemblage should allow for the reconstruction of different past upwelling regimes.

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Abiotic ammonification and gross ammonium photoproduction in the upwelling system off central Chile (36° S)

Biogeosciences Discussions ◽

10.5194/bgd-9-18479-2012 ◽

2012 ◽

Vol 9 (12) ◽

pp. 18479-18518

Author(s):

A. Rain-Franco ◽

C. Muñoz ◽

C. Fernandez

Keyword(s):

Organic Matter ◽

Coastal Upwelling ◽

Archaeal Community ◽

Simultaneous Occurrence ◽

Diatom Species ◽

Chaetoceros Muelleri ◽

Central Chile ◽

Upwelling System ◽

Simulated Solar Radiation ◽

Radiation Conditions

Abstract. We investigated the production of ammonium via photodegradation of dissolved organic matter (DOM) in the coastal upwelling system off central Chile (36° S). Photoammonification experiments were carried out using exudates obtained from representative diatom species (Chaetoceros muelleri and Thalassiosira minuscule) and natural marine DOM under simulated solar radiation conditions. Additionally, we evaluated the use of photoproduced ammonium by natural microbial communities and separated ammonium oxidizing archaea and bacteria by using GC-7 as an inhibitor of the archaeal community. We found photoammonification operating at two levels: via the transformation of DOM by UV radiation (abiotic ammonification) and via the simultaneous occurrence of abiotic phototransformation and biological remineralization of DOM into NH4+ (referred as gross photoproduction of NH4+). The maximum rates of abiotic ammonification reached 0.057 μmol L−1 h−1, whereas maximum rates of gross photoproduction reached 0.746 μmol L−1 h−1. Our results also suggest that ammonium oxidizing archaea could dominate the biotic remineralization induced by photodegradation of organic matter and consequently play an important role in the local N cycle. Abiotic ammonium photoproduction in coastal upwelling systems could support between 7 and 50% of the spring-summer phytoplankton NH4+ demand. Surprisingly, gross ammonium photoproduction (remineralization induced by abiotic ammonification) might support 50 to 180% of spring-summer phytoplankton NH4+ assimilation.

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Spatial and temporal variation in barnacle growth in a coastal upwelling system

Marine Ecology Progress Series ◽

10.3354/meps209143 ◽

2001 ◽

Vol 209 ◽

pp. 143-157 ◽

Cited By ~ 67

Author(s):

E Sanford ◽

BA Menge

Keyword(s):

Temporal Variation ◽

Coastal Upwelling ◽

Spatial And Temporal Variation ◽

Upwelling System

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The Benguela Upwelling System: Quantifying the Sensitivity to Resolution and Coastal Wind Representation in a Global Climate Model*

Journal of Climate ◽

10.1175/jcli-d-15-0192.1 ◽

2015 ◽

Vol 28 (23) ◽

pp. 9409-9432 ◽

Cited By ~ 69

Author(s):

R. Justin Small ◽

Enrique Curchitser ◽

Katherine Hedstrom ◽

Brian Kauffman ◽

William G. Large

Keyword(s):

Wind Stress ◽

Climate Model ◽

Coastal Upwelling ◽

Ocean Model ◽

Wind Stress Curl ◽

Upwelling System ◽

Wind Structure ◽

Eastern Boundary ◽

Benguela Upwelling ◽

Atmosphere Model

Abstract Of all the major coastal upwelling systems in the world’s oceans, the Benguela, located off southwest Africa, is the one that climate models find hardest to simulate well. This paper investigates the sensitivity of upwelling processes, and of sea surface temperature (SST), in this region to resolution of the climate model and to the offshore wind structure. The Community Climate System Model (version 4) is used here, together with the Regional Ocean Modeling System. The main result is that a realistic wind stress curl at the eastern boundary, and a high-resolution ocean model, are required to well simulate the Benguela upwelling system. When the wind stress curl is too broad (as with a 1° atmosphere model or coarser), a Sverdrup balance prevails at the eastern boundary, implying southward ocean transport extending as far as 30°S and warm advection. Higher atmosphere resolution, up to 0.5°, does bring the atmospheric jet closer to the coast, but there can be too strong a wind stress curl. The most realistic representation of the upwelling system is found by adjusting the 0.5° atmosphere model wind structure near the coast toward observations, while using an eddy-resolving ocean model. A similar adjustment applied to a 1° ocean model did not show such improvement. Finally, the remote equatorial Atlantic response to restoring SST in a broad region offshore of Benguela is substantial; however, there is not a large response to correcting SST in the narrow coastal upwelling zone alone.

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