Regional ecosystem dynamics in the ACC: simulations with a three-dimensional ocean-plankton model

Hense, Inga; Timmermann, Ralph; Beckmann, Aike; Bathmann, Ulrich

doi:10.1016/s0924-7963(03)00063-0

Cited by 17 publications

(19 citation statements)

References 78 publications

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“…2b). Such a pattern is typical not only for coastal upwelling situations but has been observed and simulated in frontal upwelling systems as well (Strass et al 2002Hense et al 2003. A weak subsurface maximum is found above the midbasin secondary nutricline which coincides with the thermocline (Fig.…”

Section: Reference Experimentssupporting

confidence: 66%

Torn between extremes: the ups and downs of phytoplankton

Beckmann

Hense

2004

Ocean Dynamics

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We present a model to investigate the success and resulting patterns of phytoplankton migration, based on motility which depends exclusively on the internal energy and nutrient state of the cells. The model consists of migrating and non-migrating sub compartments for phytoplankton, and migration is a function of the prescribed threshold values for internal quotas. The different modes of phytoplankton behavior are evaluated in the framework of a coupled physical-biological model that includes wind-driven up-and downwelling. The results show that (1) migration is almost always advantageous with respect to biomass, (2) a wide variety of migration patterns (e.g., subsurface maxima, surfaceavoidance behavior) can be reproduced by a relatively simple treatment of motility, (3) multiple deep chlorophyll maxima can be explained as the result of certain threshold values in combination with negligible vertical movement of the water, and (4) descending tongues of high phytoplankton concentration may be caused by migratory behavior and not necessarily by subduction due to frontal convergence. Thus, our model offers explanations for a large variety of observed phytoplankton distributions and migration patterns.

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Section: Reference Experimentssupporting

confidence: 66%

Torn between extremes: the ups and downs of phytoplankton

Beckmann

Hense

2004

Ocean Dynamics

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“…Upwelling and downwelling motions were observed in the meandering of the PF [ Strass et al ., ]. An ocean‐plankton model suggests that due to the fast surface currents of the ACC, enhanced Chl‐a can occasionally occur in downwelling areas, and low Chl‐a can occur in upwelling areas [ Hense et al ., ]. This is because newly upwelled water near the surface has low Chl‐a, but it is rich in nutrients and therefore can sustain phytoplankton growth while it is advected, and until a downwelling event occurs.…”

Section: Resultsmentioning

confidence: 99%

“…Nutrient supply in the Southern Ocean is thought to be controlled by ocean dynamics [e.g., de Baar et al ., ; Hense et al ., ; Fennel et al ., ; Moore , ; Meskhidze et al ., ]. Physical processes such as mixing, upwelling, horizontal advection, secondary circulation associated with mesoscale features (i.e., eddies and fronts), and entrainment due to changes in the mixed‐layer depth (MLD), all can contribute to the supply of nutrients to the euphotic zone.…”

Section: Introductionmentioning

confidence: 99%

Southern Ocean wind‐driven entrainment enhances satellite chlorophyll‐a through the summer

2015

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Despite being the largest High Nitrate Low Chlorophyll (HNLC) region, the Southern Ocean sustains phytoplankton blooms through the summer, when presumably there is sufficient light, but nutrients in the euphotic zone have been depleted. Physical processes that can potentially supply nutrients from subsurface waters to the euphotic zone, and promote phytoplankton growth in the summer, have not been fully explored at the large scale. By means of a correlation analysis, this study combines high-resolution satellite observations of ocean color, winds and sea surface temperature, surface heat fluxes from reanalysis and Argo mixed-layer depth (MLD) estimates to explore the role of the atmospheric forcing (i.e., winds and surface heat fluxes) on upper ocean processes that may help sustain high satellite chlorophyll-a (Chl-a) through the summer. Two physical processes that can supply nutrients to the euphotic zone are: MLD deepening, caused by wind-mixing and/or surface cooling, and Ekman pumping driven by the wind stress curl. We find that high winds correlate with high Chl-a over broad open ocean areas, suggesting that transient MLD deepening through wind-mixing (i.e., wind-driven entrainment) helps sustain high Chl-a. Wind-driven entrainment plays a dominant role on time scales associated with atmospheric synoptic storms (i.e., <10 days) and has a larger influence on surface Chl-a than storm scale local Ekman pumping. Based on our analysis of statistically significant correlation patterns, we identify regions in the Southern Ocean where wind-induced entrainment may play a role in sustaining summer phytoplankton blooms.

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“…The high variability of abundance in particle‐associated Flavobacteria (Fig. 2(b)) may derive from localized patchiness of phytoplankton populations in the Southern Ocean due to the effects of advection, iron and silica nutrient limitation[39], as well as competition with other bacteria, in particular Proteobacteria.…”

Section: Discussionmentioning

confidence: 99%

Ecological and biogeographic relationships of class Flavobacteria in the Southern Ocean

Abell

Bowman

2005

FEMS Microbiology Ecology

181

167

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The abundance, spatial distribution and diversity of class Flavobacteria were investigated in the Southern Ocean euphotic zone across a latitudinal transect and in the ice pack off Eastern Antarctica. Surface seawater samples filter-fractionated into 0.8 mum particulate and 0.2 m planktonic fractions were investigated with different molecular techniques. The abundance of particle-associated Flavobacteria, ascertained with real-time PCR and DGGE band analysis using Flavobacteria-specific primers, was found to be significantly higher in Polar Front Zone (PFZ) and Antarctic Zone (AZ) water samples than in nutrient limited Temperate Zone (TZ) and Sub-Antarctic Zone (SAZ) waters. Abundance of particle-associated Flavobacteria correlated positively with seawater chlorophyll a and nutrient concentrations, suggesting that increased Flavobacteria abundance may relate to enhanced primary production in the PFZ and AZ. This is supported by comparison of DGGE profiles that demonstrated significant differences in the total Flavobacteria community structure and 16S rRNA gene diversity between samples from the PFZ and AZ and those from TZ and SAZ. Sequence analysis revealed a broad diversity amongst class Flavobacteria in the Southern Ocean with several Flavobacteria clades detected in PFZ and AZ waters not detected in TZ and SAZ waters that putatively represent psychrophilic taxa. Sequence data included a large, so far uncultivated, cosmopolitan phylogenetic clade ("DE cluster 2") that is distributed throughout the Southern Ocean.

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Regional ecosystem dynamics in the ACC: simulations with a three-dimensional ocean-plankton model

Cited by 17 publications

References 78 publications

Torn between extremes: the ups and downs of phytoplankton

Torn between extremes: the ups and downs of phytoplankton

Southern Ocean wind‐driven entrainment enhances satellite chlorophyll‐a through the summer

Ecological and biogeographic relationships of class Flavobacteria in the Southern Ocean

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