Phytoplankton biomass and primary production in Delagoa Bight Mozambique: Application of remote sensing

Kyewalyanga, Margareth S.; Naik, Krishna; Hegde, Sahana; Raman, Mini; Barlow, Ray; Roberts, Mike

doi:10.1016/j.ecss.2007.04.027

Cited by 21 publications

(12 citation statements)

References 17 publications

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“…There is agreement between Pathfinder and ROMS-SWIM in showing cooler mean SST in Delagoa Bight. In the Bight, surface water varies in ROMS-SWIM between 21.5°C in winter to 28°C in summer (not shown) in agreement with observations [Kyewalyanga et al, 2007;Barlow et al, 2008;Lamont et al, 2010].…”

Section: Modelled Regional Mean Ocean Circulation Sst and Eddy Energysupporting

confidence: 84%

Modelling cyclonic eddies in the Delagoa Bight region

Cossa

Pous

Penven

et al. 2016

Continental Shelf Research

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International audienceThe objective of this study is to document and shed light on the circulation around the Delagoa Bight region in the southern Mozambique Channel using a realistic modelling approach. A simulation including mesoscale forcings at the boundaries of our regional configuration succeeds in reproducing the general circulation in the region as well as the existence of a semi-permanent cyclonic eddy, whose existence is attested by in situ measurements in the Bight. Characterised by a persistent local minimum in SSH located around 26°S—34°E, this cyclonic eddy termed herein the Delagoa Bight lee eddy occurs about 25% of the time with no clear seasonal preference. Poleward moving cyclones, mostly generated further north, occur another 25% of the time in the Bight area. A tracking method applied to eddies generated in Delagoa Bight using model outputs as well as AVISO data confirms the model realism and provides additional statistics. The diameter of the eddy core varies between 61 and 147 km and the average life time exceeds 20 days. Additional model analyses reveal the systematic presence of negative vorticity in the Bight that can organise and form a Delagoa Bight lee eddy depending on the intensity of an intermittent southward flow along the shore and the spatial distribution of surrounding mesoscale features. In addition, the model solution shows other cyclonic eddies generated near Inhambane and eventually travelling through the Bight. Their generation and pathways appears to be linked with large Mozambique Channel rings

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Section: Modelled Regional Mean Ocean Circulation Sst and Eddy Energysupporting

confidence: 84%

Modelling cyclonic eddies in the Delagoa Bight region

Cossa

Pous

Penven

et al. 2016

Continental Shelf Research

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“…Their results suggested that there is an area in the Delagoa Bight, the Inharrime terrace, where upwelling enhances biological productivity over the continental shelf. A later study by Kyewalyanga et al (2007) using satellite ocean color products and a biological model corroborated this finding. Lutjeharms https://doi.org/10.5194/bg-2020-486 Preprint.…”

Section: Historical Perspectivesmentioning

confidence: 62%

Reviews and syntheses: Physical and biogeochemical processes associated with upwelling in the Indian Ocean

Vinayachandran¹,

Masumoto²,

Roberts³

et al. 2021

Preprint

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Abstract. The Indian Ocean presents two distinct climate regimes. The North Indian Ocean is dominated by the monsoons, whereas the seasonal variation is less pronounced in the south. The prevailing wind pattern produces upwelling along different parts of the coast in both hemispheres during different times of the year. Additionally, dynamical processes and eddies either cause or enhance upwelling. This paper reviews the phenomena of upwelling along the coast of the Indian Ocean extending from the tip of South Africa to the southern tip of the west coast of Australia. Observed features, underlying mechanisms, and the impact of upwelling on the ecosystem are presented. In the Agulhas Current region, cyclonic eddies associated with the Natal pulses drive slope upwelling and enhances chlorophyll concentration along the continental margin. The Durban break-away eddy spun-up by the Agulhas upwells cold nutrient-rich water. Besides, topographically induced upwelling occurs along the inshore edges of Agulhas Current. Wind-driven coastal upwelling occurs along the South coast of Africa and augments the dynamical upwelling in the Agulhas Current. Upwelling hotspots along Mozambique are present in the northern and southern sectors of the channel, and they are ascribed to dynamical effects of ocean circulation in addition to wind forcing. Interaction of mesoscale eddies with the western boundary, anticyclonic eddy pair interactions, and passage of cyclonic eddies cause upwelling. Upwelling along the southern coast of Madagascar is caused by Ekman wind-driven mechanism and by eddy generation and inhibited by Southwest Madagascar Coastal Current. The seasonal upwelling that occurs along the East African coast is primarily driven by the Northeast monsoon winds and enhanced by topographically induced shelf-breaking and shear instability between the East African Coastal Current and the island chains. Somali coast presents a strong case for the classical Ekman type of upwelling. This upwelling can be inhibited by the arrival of deeper thermocline signals generated in the offshore region by wind stress curl. The upwelling is nearly uniform along the coast of Arabia, it is caused by the alongshore component of the summer monsoon winds and modulated by the arrival of Rossby waves generated in the offshore region by cyclonic wind stress curl. Along the west coast of India, upwelling is driven by coastally trapped waves together with the alongshore component of the southwesterlies. Along the southern tip of India and Sri Lanka, the strong Ekman transport dives upwelling. Upwelling is feeble along the east coast of India and occurs during the summer, caused by alongshore winds. In addition, mesoscale eddies lead to upwelling but the arrival of river water plumes inhibits upwelling along this coast. Southeasterly winds drive upwelling along the coast of Sumatra and Java during summer. Kelvin wave propagation originating from the Equatorial Indian Ocean affects the magnitude and extent of Sumatra and Java upwelling. Both ENSO and IOD events cause large variability of upwelling here. Along the west coast of Australia, southerly winds can dominate over the Leeuwin Current, causing sporadic upwelling, which is prominent along the southwest, central, and Gascoyne coasts during summer. The open ocean upwelling in the southern tropical Indian Ocean and within the Sri Lanka Dome is driven primarily by the wind stress curl but also impacted by Rossby wave propagations. Upwelling is a key driver in enhancing biological productivity in all sectors of the coast, as indicated by enhanced sea surface chlorophyll concentrations. Additional knowledge at varying levels has been gained through in situ observations and model simulations. In the Mozambique channel, upwelling simulates new production, and circulation redistributes the production generated by upwelling and mesoscale eddies leading to observations of higher ecosystem impact along the edges of eddies. Similarly, along the southern Madagascar coast, biological connectivity is influenced by the transport of phytoplankton from upwelling zones. Along the coast of Kenya, both productivity rates and zooplankton biomass are higher during the upwelling season. Along the Somali coast, accumulation of upwelled nutrients in the northern part of the coast leads to spatial inhomogeneity in productivity. On the other hand, productivity is more uniform along the coasts of Yemen and Oman. Upwelling along the west coast of India has several biogeochemical implications, including oxygen depletion, denitrification, and high production of CH4 and dimethyl sulfide. Though feeble, wind-driven upwelling leads to significant enhancement of phytoplankton in the northwest Bay of Bengal during the summer monsoon. Along the Sumatra and Java coasts, upwelling affects the phytoplankton composition and assemblages. Dissimilarities in copepod assemblages occur during the upwelling periods along the west coast of Australia. Phytoplankton abundance characterizes inshore edges of the slope during upwelling season, and upwelling eddies are associated with abundance in Krill. The review identifies the northern coast of the Arabian Sea and eastern coasts of the Bay of Bengal as the least observed sectors. Further, sustained long-term observations with high temporal and spatial resolutions along with high-resolution modeling efforts are suggested for a proper description of upwelling, its variability, and its relationship to the ecosystem.

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“…In comparison to the Benguela system, far fewer studies on phytoplankton have been conducted in the Agulhas region (AR), with the majority of investigations focussed on the wider shelf areas of the KwaZulu-Natal (KZN) Bight (28.5-30 °S) and the Delagoa Bight (~24-27 °S). Early studies showed Chla concentrations in Delagoa Bight ranging between 0.6 and 1.26 mg m -3 (Mordasova, 1980), and more recent investigations (Barlow et al 2008;Kyewalyanga et al, 2007;Sá et al, 2013) have illustrated variable phytoplankton distributions in response to changing circulation patterns (Lamont et al, 2010). On the KZN shelf, a wide range of in situ Chla concentrations has been observed (Barlow et al, 2008(Barlow et al, , 2010(Barlow et al, , 2013(Barlow et al, , 2015Burchall, 1968 a, b;Carter and Schleyer, 1988).…”

Section: East Coast Of Southern Africa and Madagascarmentioning

confidence: 99%

Seasonal variation in remotely-sensed phytoplankton size structure around southern Africa

Lamont

Brewin

Barlow

2018

Remote Sensing of Environment

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The three-component model of Brewin et al. (2010) computes fractional contributions of three phytoplankton size classes (micro-(> 20 m), nano-(2-20 m), picophytoplankton (< 2 m)) to the overall chlorophyll a concentration (Chla). Using in situ pigment data, model coefficients were adjusted for application to the southern African marine region. The refined model was applied to seasonal and monthly climatologies of MODIS Aqua Chla around Southern Africa. Chla > 1 mg m-3 was limited to shelf regions along the coasts of Southern Africa and Madagascar, while values < 0.1 mg-3 were found over most of the open ocean between the equator and 38 °S during austral summer and autumn. In winter and spring, low values (< 0.1 mg m-3) were restricted to smaller regions within subtropical gyres, while values up to 0.7 mg m-3 extended over a much greater area of the open ocean. Shelf regions in the northern (NB) and southern Benguela (SB), Agulhas Bank (AB), Agulhas region (AR), and Mozambique Channel (MC) all showed similar seasonal cycles of size structure. On average, micro-phytoplankton comprised > 50 % of the total Chla in these regions with little change throughout the year. The AR shelf differed, with picophytoplankton dominating in summer, and micro-and nanophytoplankton the rest of the year. In the open ocean domains of the NB, SB, and AB regions, nanophytoplankton dominated for most of the year, with picophytoplankton being more prevalent during summer and autumn. In contrast, in the AR open ocean, nanophytoplankton were dominant only during winter and early spring, whereas picophytoplankton dominated throughout the year in the MC open ocean. The refined model characterised previously unknown spatial and temporal changes in size structure in various ecosystems around Southern Africa.

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Phytoplankton biomass and primary production in Delagoa Bight Mozambique: Application of remote sensing

Cited by 21 publications

References 17 publications

Modelling cyclonic eddies in the Delagoa Bight region

Modelling cyclonic eddies in the Delagoa Bight region

Reviews and syntheses: Physical and biogeochemical processes associated with upwelling in the Indian Ocean

Seasonal variation in remotely-sensed phytoplankton size structure around southern Africa

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