Oceans and Coastal Research

Cape Town, South Africa

Oceans and Coastal Research

Cape Town, South Africa
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Barlow R.,Bayworld Center for Research and Education | Barlow R.,University of Cape Town | Lamont T.,University of Cape Town | Lamont T.,Oceans and Coastal Research | And 4 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2016

A study of phytoplankton in a cyclonic eddy was undertaken in the Mozambique Basin between Madagascar and southern Africa during austral winter. CHEMTAX analysis of pigment data indicated that the community comprised mainly haptophytes and diatoms, with Prochlorococcus, prasinophytes and pelagophytes also being prominent to the east and west of the eddy. There was little difference in community structure, chlorophyll-specific absorption [a*ph(440)] and pigment:TChla ratios between the surface and the sub-surface chlorophyll maximum (SCM), reflecting acclimation to fluctuating light conditions in a well mixed upper layer. Values for a*ph(440) were low for diatom dominance, high where prokaryote proportion was high, and intermediate for flagellate dominated communities. Chlorophyll c and fucoxanthin:TChla ratios were elevated over most of the eddy, while 19'-hexanoyloxyfucoxanthin ratios increased in the eastern and western sectors. In a community comprising mainly flagellates and Prochlorococcus to the west of the eddy, there was high a*ph(440) at the surface and elevated ratios for divinyl chlorophyll a, chlorophyll b and 19'-hexanoyloxyfucoxanthin at the SCM. An increase in diadinoxanthin:TChla ratios and a decline in the quantum efficiency of photochemistry in PSII under high light conditions, indicated some photoprotection and photoinhibition at the surface even in a well mixed environment. Diadinoxanthin was the main photoprotective carotenoid within the eddy, while zeaxanthin was the dominant photoprotective pigment outside the eddy. The results of this study will be useful inputs into appropriate remote sensing models for estimating primary production and the size class distribution of phytoplankton in eddies in the southwest Indian Ocean. © 2017 Elsevier Ltd.

Morris T.,South African Environmental Observation Network | Hermes J.,South African Environmental Observation Network | Beal L.,University of Miami | Du Plessis M.,University of Cape Town | And 7 more authors.
South African Journal of Science | Year: 2017

The 2013 Intergovernmental Panel on Climate Change report, using CMIP5 and EMIC model outputs suggests that the Atlantic Meridional Overturning Circulation (MOC) is very likely to weaken by 11-34% over the next century, with consequences for global rainfall and temperature patterns. However, these coupled, global climate models cannot resolve important oceanic features such as the Agulhas Current and its leakage around South Africa, which a number of studies have suggested may act to balance MOC weakening in the future. To properly understand oceanic changes and feedbacks on anthropogenic climate change we need to substantially improve global ocean observations, particularly within boundary current regions such as the Agulhas Current, which represent the fastest warming regions across the world's oceans. The South African science community, in collaboration with governing bodies and international partners, has recently established one of the world's most comprehensive observational networks of a western boundary current system, measuring the Greater Agulhas Current System and its inter-ocean exchanges south of Africa. This observational network, through its design for long-term monitoring, collaborative coordination of resources and skills sharing, represents a model for the international community. We highlight progress of the new Agulhas System Climate Array, as well as the South African Meridional Overturning Circulation programme, which includes the Crossroads and GoodHope hydrographic transects, and the South Atlantic MOC Basin-wide Array. We also highlight some of the ongoing challenges that the programmes still face. © 2017 The Author(s).

Vinas M.D.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero | Blanco-Bercial L.,University of Connecticut | Bucklin A.,University of Connecticut | Verheye H.,Oceans and Coastal Research | And 3 more authors.
Journal of Experimental Marine Biology and Ecology | Year: 2015

Calanoides carinatus sensu lato (s.l.) (Krøyer, 1848) is known to occur in the North and South Atlantic, Indian, and tropical western Pacific Oceans, and the Mediterranean Sea. In highly productive areas, this species may dominate the copepod biomass and occupy a pivotal position in the pelagic food webs that support commercial fisheries. Despite the species' ecological importance, its taxonomic status and biogeographic range are not certain. An international collaborative project was carried out to examine the molecular phylogeography and population genetics of C. carinatus of the Atlantic Ocean. A total of 55 specimens were identified from 13 samples collected from neritic populations of the SW (23°S-47°S), SE (16°S-34°S) and NE (11°N-44°N) Atlantic Ocean. A 708 base-pair (bp) region of the mitochondrial cytochrome c oxidase subunit I (mtCOI) gene was amplified. DNA sequences were trimmed to a final aligned length of 484bp for analysis. A parsimony haplotype network (constructed with TCS Ver. 1.2.1) had no shared haplotypes between the SE and SW Atlantic samples. In contrast, SE and NE Atlantic samples had broadly shared haplotypes, although several individuals from the NE Atlantic had very divergent haplotypes. Based on all samples analyzed, neutrality tests were both positive and significant (Tajima's D=2.374, p<0.05; Fu's FS=29.378, p<0.001) and haplotype diversity (Hd) was 0.81. NE and SE Atlantic samples were pooled for analysis (based on average pairwise Tamura-Nei distance between C. carinatus s.l. individuals=0.024). Between SW and NE/SE Atlantic populations, average pairwise distance=0.556 and ϕST=0.956 (p<0.0001). Phylogeographic analysis of mtCOI sequence variation indicates that C. carinatus s.l. comprises two genetically divergent and geographically distinct species. Since the type locality of the species is in Brazilian waters, we consider the SW Atlantic type to represent C. carinatus sensu stricto (s.s.), with a biogeographical range restricted to the SW Atlantic Ocean. Further, we consider the NE/SE Atlantic type to be an undescribed, cryptic sibling species. © 2015 Elsevier B.V.

Brewin R.J.W.,Plymouth Marine Laboratory | Brewin R.J.W.,National Center for Earth Observation | Sathyendranath S.,Plymouth Marine Laboratory | Sathyendranath S.,National Center for Earth Observation | And 7 more authors.
Remote Sensing of Environment | Year: 2015

Phytoplankton size structure is an important indicator of the state of the pelagic ecosystem. Stimulated by the paucity of in situ observations on size structure, and by the sampling advantages of autonomous remote platforms, new efforts are being made to infer the size-structure of the phytoplankton from oceanographic variables that may be measured at high temporal and spatial resolution, such as total chlorophyll concentration. Large-scale analysis of in situ data has revealed coherent relationships between size-fractionated chlorophyll and total chlorophyll that can be quantified using the three-component model of Brewin et al. (2010). However, there are variations surrounding these general relationships. In this paper, we first revise the three-component model using a global dataset of surface phytoplankton pigment measurements. Then, using estimates of the average irradiance in the mixed-layer, we investigate the influence of ambient light on the parameters of the three-component model. We observe significant relationships between model parameters and the average irradiance in the mixed-layer, consistent with ecological knowledge. These relationships are incorporated explicitly into the three-component model to illustrate variations in the relationship between size-structure and total chlorophyll, ensuing from variations in light availability. The new model may be used as a tool to investigate modifications in size-structure in the context of a changing climate. © 2015 Elsevier Inc.

Barlow R.,Bayworld Center for Research and Education | Barlow R.,University of Cape Town | Gibberd M.-J.,University of Cape Town | Lamont T.,University of Cape Town | And 3 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2016

Surface pigment data from a transect along the eastern boundary of the Atlantic Ocean was analysed using CHEMTAX to yield more detailed information on the composition of phytoplankton communities. Total chlorophyll a concentrations varied from 0.03 mg m-3 in a northern oligotrophic region to 30.3 mg m-3 in the Benguela ecosystem. Diatoms dominated the Benguela, while both diatoms and haptophytes were the major groups in the Canary ecosystem and the temperate NE Atlantic. Prochlorococcus was the most prominent group in the southern oligotrophic region (15.5°S-15°N) although haptophytes were also a significant component of the population. In contrast, haptophytes dominated the northern oligotrophic region (21°-40°N). Photo-pigment indices indicated that chlorophyll b was mainly associated with prasinophytes and chlorophyll c with diatoms. Elevated photosynthetic carotenoids were due to increased proportions of haptophytes, but also linked with diatoms and dinoflagellates. Photoprotective carotenoids were more prominently associated with Prochlorococcus and to a lesser extent to Synechococcus. © 2016 Elsevier Ltd.

Lebourges-Dhaussy A.,French National Center for Scientific Research | Huggett J.,Oceans and Coastal Research | Huggett J.,University of Cape Town | Ockhuis S.,Cape Peninsula University of Technology | And 4 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2014

Two surveys were conducted in the Mozambique Channel in November 2009 and April/May 2010 to study the influence of mesoscale eddies on the zooplanktonic component of the ecosystem. Three complementary methods were used to sample zooplankton: (1) hydro-acoustics with a TAPS™ multi-frequency zooplankton profiler; (2) in situ biological sampling using a Multinet with samples processed via the classical settled biovolume technique; (3) ZooScan image analysis which determines biovolume, size and taxonomic composition. This approach presented an ideal opportunity to compare the results of these different methods which highlighted a large overlap in their detectable size range. Each method favoured a particular size fraction of the population, i.e. TAPS for the microzooplankton (<0.1. mm ESR) and the Multinet and ZooScan for larger sizes (>3. mm ESR). In the case of the 2009 cruise, a well-established cyclone-anticyclone dipole was sampled, with results clearly indicating a higher concentration of zooplankton in the cyclonic eddy compared to the anticyclonic counterpart. The TAPS also detected high surface (0-22. m) concentrations of what appeared to be microzooplankton or marine snow in the cyclone. In 2010, the eddy field was less defined and more spatially variable compared to that in 2009. Two cyclonic and anticyclonic features were sampled during the cruise, each with different life histories and levels of stability. Results were inconsistent compared to those of 2009 and dependent on the size component of the population, with both cyclonic and anticyclonic features capable of having higher planktonic biomass. Differences in species composition between these mesoscale features were not too different and mainly a matter of relative biovolume. Less well formed eddy fields, particularly in the mid-Mozambique Channel, therefore appear to result in indistinct vertical and horizontal zooplankton distribution patterns. © 2013 Elsevier Ltd.

Lamont T.,Oceans and Coastal Research | Lamont T.,University of Cape Town | Van Den Berg M.A.,Oceans and Coastal Research | Barlow R.G.,University of Cape Town | Barlow R.G.,Bayworld Center for Research and Education
Journal of Physical Oceanography | Year: 2016

The Agulhas Current is a fast western boundary current flowing along the South African east coast, strongly influencing oceanographic variability on the adjacent KwaZulu-Natal shelf. Hydrographic observations in January 2010, July 2010, and July 1989 have been used to describe variations in geostrophic currents and water masses and to elucidate mechanisms of change in circulation and thermohaline structure. Differences in wind forcing, precipitation, and solar insolation caused modifications in stratification and mixing that resulted in seasonal changes in surface temperature, salinity, and mixed layer depth ZMLD between the austral summer and winter surveys. During January 2010, surface temperatures were elevated and there was a large range in salinity as the upper 10 m was influenced by river outflow and rainfall. In July 2010 and 1989, surface temperatures were lower and the salinity range was significantly less. The ZMLD in January 2010 was much shallower, varying between 5 and 40 m, while deeper ZMLD, from 9 to 107 m, was found in July 2010 and 1989. Cross-shelf, alongshore, and vertical variations in water masses during July 2010 and July 1989 were driven by deviations in the position of the inshore edge of the Agulhas Current and the influence of offshore cyclonic eddies. In January 2010, the close proximity of the current to the coast and shelf break caused increased Ekman veering in the bottom layers along the shelf edge and slope in the north and recirculation in the south. © 2016 American Meteorological Society.

Lamont T.,Oceans and Coastal Research | Lamont T.,University of Cape Town | Barlow R.G.,Bayworld Center for Research and Education | Barlow R.G.,University of Cape Town | Kyewalyanga M.S.,University of Dar es Salaam
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2014

Investigations of primary production (PP) were undertaken in the southern Benguela ecosystem during two research surveys in October 2006 and May 2007. Significant differences in environmental conditions, as well as biomass and PP, were observed between October and May. During October, integrated biomass and PP were significantly higher, ranging from 20.43 to 355.01mgm-2, and 0.71 to 6.98gCm-2d-1, respectively, than in May, where the range was 47.92-141.79mgm-2, and 0.70-3.35gCm-2d-1, respectively. Distribution patterns indicated low biomass and PP in newly upwelled water along the coast, higher biomass and PP in the mid-shelf region, while lower values were observed at and beyond the shelf edge. Latitudinal variations showed consistently higher biomass and PP in the St. Helena Bay region compared to biomass and PP south of Cape Town. During both surveys, phytoplankton communities were comprised primarily of diatoms and small flagellates, with no significant differences. Phytoplankton adaptation to environmental variability was characterised by increased Pm B and Ek under elevated temperatures and irradiance, while no clear relationships were evident for αB. Generalised Additive Models (GAMs) showed that photosynthetic parameters were all significant predictors of photosynthesis rates (Pz), with Pm B being the most important, accounting for 36.97% of the deviance in Pz. However, biomass levels and environmental conditions exerted a much greater influence on Pz, with irradiance explaining the largest proportion (68.24%) of the deviance. Multiple predictor GAMs revealed that 96.26% of the deviance in Pz could be explained by a model which included nitrate, chlorophyll a, and irradiance. © 2014 Elsevier Ltd.

Verheye H.M.,Oceans and Coastal Research | Verheye H.M.,University of Cape Town | Lamont T.,Oceans and Coastal Research | Lamont T.,University of Cape Town | And 4 more authors.
Environmental Development | Year: 2015

Environmental drivers that have been observed to cause changes in phytoplankton biomass and production include surface warming, increased wind stress and upwelling, extension of low oxygen zones, changes in nutrient distributions, and increased stratification. While there have been documented variations in phytoplankton biomass and primary production at seasonal and interannual time scales in the BCLME, there appears to be no strong evidence of decade-scale changes or the expected ecosystem-wide increase/decrease in production in response to projected increases/decreases in upwelling-favourable winds. During the past six decades there have been substantial, long-term changes in abundance, biomass, production and species and size composition of neritic zooplankton communities in both the northern and southern Benguela subsystems. Copepods have increased since the 1950s in both subsystems, until a turning point around the mid-1990s in the south and a decade later in the north, after which they have been declining. Both subsystems also experienced a shift from large to smaller species dominating. These major changes reflect patterns of spatial, temporal and size-based heterogeneity in the BCLME and are thought to be mediated locally and differentially through bottom-up and top-down forcing mechanisms. While the relative importance of these control mechanisms remains uncertain, changes in the plankton as observed in the BCLME have fundamental effects on biogeochemical processes, food web structure and ecosystem functioning, as well as on the ecosystem services supported by the plankton. Because plankton are ideal indicators of ecosystem change, continued transboundary monitoring of their communities in the BCLME is warranted in the long term, e.g. using cost-effective technologies such as satellite imagery of ocean colour and the deployment of Continuous Plankton Recorders from ships-of-opportunity. © 2015 Elsevier Ltd.

De Villiers S.,Oceans and Coastal Research | Siswana K.,Oceans and Coastal Research | Vena K.,Oceans and Coastal Research
Earth System Science Data | Year: 2015

Several open-ocean mesoscale features - a "young" warm-core (anti-cyclonic) eddy at 52° S, an "older" warm-core eddy at 57.5° S and an adjacent cold-core (cyclonic) eddy at 56° S - were surveyed during a R/V S.A. Agulhas II cruise in April 2014. The main aim of the survey was to obtain hydrographical and biogeochemical profile data for contrasting open-ocean eddies in the Southern Ocean, which will be suitable for comparative study and modelling of their heat, salt and nutrient characteristics, and the changes that occur in these properties as warm-core eddies migrate from the polar front southwards. The major result is that the older warm-core eddy at 57.5° S is, at its core, 2.7° C colder than a younger eddy at 52° S, while its dissolved silicate levels are almost 500 % higher and accompanied by chlorophyll a levels that are more than 200 % higher than that in the younger eddy. A total of 18 CTD stations were occupied in a sector south of the Southwest Indian Ridge, along three transects crossing several mesoscale features identified from satellite altimetry data prior to the cruise. The CTD data, as well as chlorophyll a and dissolved nutrient data (for NO3 -, NO2 -, PO4 3- and SiO2), have been processed, quality controlled and made available via the PANGAEA Data Archiving and Publication database at doi:10.1594/PANGAEA.848875. © Author(s) 2015.

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