Ocean climate of the South East Atlantic observed from satellite data and wind models

Hardman-Mountford, NJ; Richardson, Anthony J.; Agenbag, J. J.; Hagen, Eberhard; Nykjær, Leo; Shillington, F. A.; Villacastin, C.

doi:10.1016/j.pocean.2003.10.001

Cited by 126 publications

(111 citation statements)

References 92 publications

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“…1 Bathymetry of the South East Atlantic overlain with climatological sea surface temperatures (contour lines, in°C) (Gouretski and Koltermann 2004). Arrows show surface (solid) and subsurface (dashed) hydrographic features (Hardman-Mountford et al 2003). SEC south equatorial current, SECC south equatorial counter current, BC benguela oceanic current, BCC benguela coastal current, ABFZ Angola-Benguela front, PU poleward undercurrent Int J Earth Sci (Geol Rundsch) (2009) 98:309-326 311 in the water column (Kuypers et al 2005;Tyrrell and Lucas 2002).…”

Section: Chemical and Biological Characteristics Of Coastal Upwellingmentioning

confidence: 99%

“…Past variability in forcing and upwelling: evidence from observations A synopsis of evidence for variations in forcing on seasonal to interannual time scales since the 1980s has been recently published by Hardman-Mountford et al (2003) for the Northern Benguela region. These authors evaluated time series of satellite data and of numerical model products.…”

Section: Nutrient Utilisation and Denitrification Intensity From D 15 Nmentioning

confidence: 99%

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Variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore Namibia: results from sediment archives

Emeis

Struck

Leipe

et al. 2007

Int J Earth Sci (Geol Rundsch)

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The coastal upwelling system offshore Namibia is ideally suited to address a focal question of the Integrated Marine Biogeochemistry and Ecosystem Research Programme: what are the mechanisms that drive long-term changes in ecosystems? Considerable interannual variability in climatic forcing is indicated by long time series of meteorological and remote sensing observation; these accompany considerable interannual to interdecadal changes in the upwelling intensity over the last 100 years, as well as a centennial trend. On longer time scales, the only archives available are sediment records spanning the late Holocene. To decipher the sediment record, we mapped surface-sediment patterns of proxies for physical (sea surface temperature/SST from alkenone unsaturation indexes) and nutrient (d 15 N on bulk sedimentary N) variables. Their present-day surface-sediment patterns outline the coastal upwelling cells and filaments and associated high productivity area. Analysed in an array of dated sediment cores, the spatial patterns of SST suggest long-term ([100 years) variability in the location and intensity of individual upwelling cells. The patterns of d 15 N outline an area of intense denitrification near the coast, and advection of water with low-oxygen concentrations in the undercurrent from the North. d 15 N exhibits considerable downcore variability, in particular over the last 50 years. The variability appears to be governed by differences in extent of denitrification and thus of the shelf oxygen balance, which appears to have deteriorated in the last 50 years. Together, the data suggest that SST and denitrification conditions have remained in the narrow bounds outlined by today's patterns in surface sediments, but that spatially small variability in upwelling intensity and make-up of upwelling feed waters induced considerable changes in the lower trophic levels of the coastal upwelling ecosystem over the last 6,000 years. Attempts to correlate proxy records from sediments with observational time series and regional climate reconstructions were not successful, possibly because annual to interannual environmental signals are erased in the process of sediment formation.

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Section: Chemical and Biological Characteristics Of Coastal Upwellingmentioning

confidence: 99%

Section: Nutrient Utilisation and Denitrification Intensity From D 15 Nmentioning

confidence: 99%

Variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore Namibia: results from sediment archives

Emeis

Struck

Leipe

et al. 2007

Int J Earth Sci (Geol Rundsch)

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“…Second, the four EBUS exhibit similar large-scale dynamics with the presence of near-coastal equatorward currents that carry relatively fresh and cold water in the surface layers from higher latitudes [Strub et al, 1998[Strub et al, , 2013Batteen et al, 2000;Hardman-Mountford et al, 2003;Mach ın et al, 2006]. This surface circulation is mainly wind-forced, but also reinforced, through geostrophic adjustment, by the cross-shore temperature (and density) gradients that separate relatively cold upwelled coastal water from warm offshore water.…”

Section: Introductionmentioning

confidence: 99%

Main eddy vertical structures observed in the four major Eastern Boundary Upwelling Systems

2015

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In the four major Eastern Boundary Upwelling Systems (EBUS), mesoscale eddies are known to modulate the biological productivity and transport near‐coastal seawater properties toward the offshore ocean, however little is known about their main characteristics and vertical structure. This study combines 10 years of satellite‐altimetry data and Argo float profiles of temperature and salinity, and our main goals are (i) to describe the main surface characteristics of long‐lived eddies formed in each EBUS and their evolution, and (ii) to depict the main vertical structure of the eddy‐types that coexist in these regions. A clustering analysis of the Argo profiles surfacing within the long‐lived eddies of each EBUS allows us to determine the proportion of surface and subsurface‐intensified eddies in each region, and to describe their vertical structure in terms of temperature, salinity and dynamic height anomalies. In the Peru‐Chile Upwelling System, 55% of the sampled anticyclonic eddies (AEs) have subsurface‐intensified maximum temperature and salinity anomalies below the seasonal pycnocline, whereas 88% of the cyclonic eddies (CEs) are surface‐intensified. In the California Upwelling System, only 30% of the AEs are subsurface‐intensified and all of the CEs show maximum anomalies above the pycnocline. In the Canary Upwelling System, ∼40% of the AEs and ∼60% of the CEs are subsurface‐intensified with maximum anomalies extending down to 800 m depth. Finally, the Benguela Upwelling System tends to generate ∼40–50% of weak surface‐intensified eddies and ∼50–60% of much stronger subsurface‐intensified eddies with a clear geographical distribution. The mechanisms involved in the observed eddy vertical shapes are discussed.

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“…The major up-welling cells of Namaqua, St. Helena Bay and the Cape Peninsula are clearly identified as areas of enhanced chl a biomass and primary productivity. Upwelling occurs during spring and summer in these seasonal cells of the southern Benguela, coinciding with the times when the trade winds are farthest south and wind in the region is strongest (Parrish et al 1983, Shannon 1985, Hardman-Mountford et al 2003. This movement of the trade winds leads to strong seasonality in integrated chl a and primary productivity off the west coast of southern South Africa (Areas 1 and 2), reaching a maximum in spring and summer (Fig.…”

Section: Possible Sources Of Error and Model Sensitivitymentioning

confidence: 87%

“…We illustrate this approach by applying it to an area off southern South Africa that includes the dynamic upwelling cells of the southern Benguela region and the warm stratified conditions of the Agulhas system (Hardman-Mountford et al 2003). Relatively few primary productivity estimates have been made in this region (but see Brown et al 1991, Probyn et al 1994, Carr et al 2002, and none have used dynamically varying chl a profiles in their estimates.…”

Section: Resale or Republication Not Permitted Without Written Consenmentioning

confidence: 99%

Generalised model of primary production in the southern Benguela upwelling system

Demarcq¹,

Richardson²,

Field³

2008

Mar. Ecol. Prog. Ser.

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We provide a proof-of-concept demonstration using a novel method for estimating depth-integrated distributions of chlorophyll from archives of data from ships, buoys or gliders combined with remotely sensed data of sea surface temperature (SST) and surface chlorophyll a (chl a) from satellites. Our area of application has contrasting hydrographic regimes, which include the dynamic southern Benguela upwelling system and the stratified waters of the Agulhas Bank, South Africa. The method involves using self-organising maps (SOMs), a type of artificial neural network, to identify 'typical' chl a profiles regardless of their statistical form, provided several of a similar shape have been found in the training set. These are arranged in a linear array, ranging from uniform profiles low in chl a to profiles with high surface or subsurface peaks. We then use generalised modelling to relate these characteristic profiles to remotely sensed surface features, viz. surface chl a and SST, as well as area, season, and water depth (a proxy for distance offshore). The model accounts for 87% of the variability in chl a profile and is used to predict the type of profile likely for each pixel in monthly remote sensing composites of SST and surface chl a and then to estimate integrated chl a and primary production with the aid of a light model. Primary production peaks in mid-summer, reaching 5 mgC m -2 d -1 locally, with an average over the whole area and all seasons of 1.4 mg C m -2 d -1. Seasonal variation is greatest in the southern part of the west coast, and lowest in the stratified southeast. Annual primary production for the southern Benguela region including the Agulhas Bank is ca. 156 million tC yr -1 . This is the most robust estimate of primary production in the Benguela system to date because it combines the spatial and temporal coverage provided by remote sensing with realistic vertical chl a profiles.KEY WORDS: Remote sensing · SeaWiFS · Ocean colour · Primary production · Self-organising maps · SOM · Generalised additive model · SOM · Vertical chlorophyll a profile Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 354: [59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74] 2008 related to their intrinsic complexity (Campbell et al. 2002), few of them directly incorporate information on the vertical distribution of phytoplankton.Sensitivity analyses of primary production models show that the error in estimates of photosynthesis can be considerable when the chlorophyll maximum is near the surface. This is generally the case in coastal upwelling areas, where profiles are variable due to the wide range of oceanic conditions from active upwelling cells and filaments inshore to stratified waters offshore.Several methods have been developed for describing non-uniform biomass profiles in the oceans. However, these methods tend to produce profile categories that are fixed for large spatial and temporal scales and may not be representative of the smaller...

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Ocean climate of the South East Atlantic observed from satellite data and wind models

Cited by 126 publications

References 92 publications

Variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore Namibia: results from sediment archives

Variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore Namibia: results from sediment archives

Main eddy vertical structures observed in the four major Eastern Boundary Upwelling Systems

Generalised model of primary production in the southern Benguela upwelling system

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