On the “hidden” phytoplankton blooms on Australia's southern shelves

Kämpf, Jochen; Kavi, Ankit

doi:10.1002/2016gl072096

Cited by 16 publications

(10 citation statements)

References 24 publications

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“…The extent and direction of the query area incorporated the direction of the river plume (interpreted from viewing monthly composite imagery across years of high flow). It also deliberately excluded a known near-shore area of seasonal upwelling, to the south-east of the study area (Auricht 2015;Kämpf 2015;Kämpf and Kavi 2017) to further exclude contributions independent of outflow. Mean concentration statistics were then extracted for each distance-from-mouth zone, and every monthly composite image for all four of the variables.…”

Section: Imagery Analysismentioning

confidence: 99%

Have droughts and increased water extraction from the Murray River (Australia) reduced coastal ocean productivity?

Auricht

Clarke

Lewis

et al. 2018

Mar. Freshwater Res.

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Abstract. River discharges are decreasing in many regions of the world; however, the consequences of this on water quality and primary productivity of receiving coastal oceans are largely unclear. We analysed satellite remote-sensing data (MODIS) of the coastal ocean zone that receives outflows from the Murray River, from 2002 to 2016. This system has experienced historical flow reductions and a recent extreme hydrological 'Millennium' drought. Remotely sensed chlorophyll-a and particulate organic carbon in the coastal ocean were strongly correlated with river outflows (R 2 . 0.6) in an 8-km radial buffer zone from the Murray Mouth, and the river influence extended up to ,60 km from the Murray Mouth during high-flow periods. This distance was approximately three times greater than the freshwater plume extent during maximum flows in 2011, suggesting that new primary productivity was created. In contrast, there was no additional coastal ocean productivity above background levels from 2007 to 2010 when river outflows ceased. Hindcast calculations based on historical flows from 1962 to 2002 suggest that declining Murray River flows have greatly reduced primary productivity in adjacent coastal waters. This has potential consequences for higher trophic levels and should be considered in future management planning.

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Section: Imagery Analysismentioning

confidence: 99%

Have droughts and increased water extraction from the Murray River (Australia) reduced coastal ocean productivity?

Auricht

Clarke

Lewis

et al. 2018

Mar. Freshwater Res.

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“…Recently, Kämpf and Kavi () examined satellite‐derived monthly chlorophyll‐a concentrations and found moderate phytoplankton blooms widespread in southern Australian shelves during autumn and early winter. In agreement, our results support the occurrence of considerable phytoplankton growth within the GAB during autumn; furthermore, they show that autumn phytoplankton growth peaks at depth and is associated with a semiannual periodicity.…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, wind‐driven upwelling events have little impact on the seasonal cycle of chlorophyll in the region as a whole (Condie & Dunn, ), contributing to productivity locally. Recently, Kämpf and Kavi () examined monthly images of satellite‐derived chlorophyll‐a concentrations and found evidence of moderate widespread autumn phytoplankton blooms, which extend across the whole width of the GAB and have the potential to sustain the top predator biomass in the GAB.…”

Section: Introductionmentioning

confidence: 99%

Nitrate Sources, Supply, and Phytoplankton Growth in the Great Australian Bight: An Eulerian‐Lagrangian Modeling Approach

et al. 2018

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The Great Australian Bight (GAB), a coastal sea bordered by the Pacific, Southern, and Indian Oceans, sustains one of the largest fisheries in Australia but the geographical origin of nutrients that maintain its productivity is not fully known. We use 12 years of modeled data from a coupled hydrodynamic and biogeochemical model and an Eulerian‐Lagrangian approach to quantify nitrate supply to the GAB and the region between the GAB and the Subantarctic Australian Front (GAB‐SAFn), identify phytoplankton growth within the GAB, and ascertain the source of nitrate that fuels it. We find that nitrate concentrations have a decorrelation timescale of ∼60 days; since most of the water from surrounding oceans takes longer than 60 days to reach the GAB, 23% and 75% of nitrate used by phytoplankton to grow are sourced within the GAB and from the GAB‐SAFn, respectively. Thus, most of the nitrate is recycled locally. Although nitrate concentrations and fluxes into the GAB are greater below 100 m than above, 79% of the nitrate fueling phytoplankton growth is sourced from above 100 m. Our findings suggest that topographical uplift and stratification erosion are key mechanisms delivering nutrients from below the nutricline into the euphotic zone and triggering large phytoplankton growth. We find annual and semiannual periodicities in phytoplankton growth, peaking in the austral spring and autumn when the mixed layer deepens leading to a subsurface maximum of phytoplankton growth. This study highlights the importance of examining phytoplankton growth at depth and the utility of Lagrangian approaches.

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“…Among the phytoplankton pigments, chlorophyll a (denoted as chlorophyll in the following description) is an important biological indicator of phytoplankton biomass in the water column. Environmental variables -such as light availability (Sverdrup, 1953;Huisman and Weissing, 1994), water temperature (Eppley, 1992;Hambright et al, 1994;Paerl and Huisman, 2008), and salinity (Karsten et al, 1995) -affect phytoplankton biomass variability. Seasonal cycles of phytoplankton concentrations are identifiable signals of the annual growth activity in pelagic systems (Cebrián and Valiela, 1999;Winder and Cloern, 2010).…”

Section: Introductionmentioning

confidence: 99%

Seasonal and inter-annual variability of water column properties along the Rottnest continental shelf, south-west Australia

et al. 2019

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A multi-year ocean glider dataset, obtained along a representative cross-shelf transect along the Rottnest continental shelf, south-west Australia, was used to characterise the seasonal and inter-annual variability of water column properties (temperature, salinity, and chlorophyll fluorescence distribution). All three variables showed distinct seasonal and inter-annual variations that were related to local and basin-scale ocean atmosphere processes. Controlling influences for the variability were attributed to forcing from two spatial scales: (1) the local scale (due to Leeuwin Current and dense shelf water cascades, DSWC) and (2) the basin scale (El Niño-Southern Oscillation, ENSO, events). In spring and summer, inner-shelf waters were well mixed due to strong wind mixing, and deeper waters ( > 50 m) were vertically stratified in temperature that contributed to the presence of a subsurface chlorophyll maximum (SCM). On the inner shelf, chlorophyll fluorescence concentrations were highest in autumn and winter. DSWCs were also the main physical feature during autumn and winter. Chlorophyll fluorescence concentration was higher closer to the seabed than at the surface in spring, summer, and autumn. The seasonal patterns coincided with changes in the wind field (weaker winds in autumn) and air-sea fluxes (winter cooling and summer evaporation). Inter-annual variation was associated with ENSO events. Lower temperatures, higher salinity, and higher chlorophyll fluorescence (> 1 mg m −3 ) were associated with the El Niño event in 2010. During the strong La Niña event in 2011, temperatures increased and salinity and chlorophyll fluorescence decreased (< 1 mg m −3 ). It is concluded that the observed seasonal and inter-annual variabilities in chlorophyll fluorescence concentrations were related to the changes in physical forcing (wind forcing, Leeuwin Current, and air-sea heat and moisture fluxes).

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On the “hidden” phytoplankton blooms on Australia's southern shelves

Cited by 16 publications

References 24 publications

Have droughts and increased water extraction from the Murray River (Australia) reduced coastal ocean productivity?

Have droughts and increased water extraction from the Murray River (Australia) reduced coastal ocean productivity?

Nitrate Sources, Supply, and Phytoplankton Growth in the Great Australian Bight: An Eulerian‐Lagrangian Modeling Approach

Seasonal and inter-annual variability of water column properties along the Rottnest continental shelf, south-west Australia

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