Upwelling and boundary circulation off Northwest Africa as depicted by infrared and visible satellite observations

Camp, Lieve Van; Nykjær, Leo; Mittelstaedt, Ekkehard; Schlittenhardt, P.

doi:10.1016/0079-6611(91)90012-b

Cited by 280 publications

(152 citation statements)

References 17 publications

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“…Additionally, very dry and warm winds (Harmattan) blow occasionally offshore from the Sahara at latitudes between 151N and 281N. These winds can carry desert dust into and over the ocean, although most of the time the boundary between the Harmattan and the maritime Trades is located over the continent parallel to the coast (Van Camp et al, 1991). In contrast, dust outbreaks which appear in boreal summer, favours dust transport from a northern source (Torres-Padró n et al, 2002).…”

Section: Introductionmentioning

confidence: 98%

“…The development and growth of the larger, permanent filaments seems to be related to changes in topography such as headlands (Strub et al, 1991). Large filaments such as those found at Cape Ghir, Cape Yubi, Cape Bojador, Cape Blanc and Mauritania (20.81N) are observable as colder jets and meanders extending several hundreds of kilometres offshore (Van Camp et al, 1991;Nykjaer and Van Camp, 1994;Barton et al, 1998;Davenport et al, 1999Davenport et al, , 2002Barton and Arístegui, 2004). Although upwelling occurs mostly on the shelf, these filaments play an important role in carbon cross-shelf transport and export to the deep ocean as has been described by Strub et al (1991), Gabric et al (1993) and Barton et al (1998).…”

Section: Introductionmentioning

confidence: 99%

“…Another important role for sedimentation in this area plays the input of dust, which is mainly controlled by the Northeast Trade Wind, the Saharan Air Layer (SAL) and the Harmattan (Sarnthein and Koopmann, 1980;Van Camp et al, 1991). Torres-Padró n et al (2002) observed a seasonal pattern of Saharan dust events with maximum fluxes in winter and summer related to two dominant meteorological scenarios.…”

Section: Introductionmentioning

confidence: 99%

“…A characteristic feature of the upwelling zone is the formation of filaments, which transport the cooler upwelled water offshore (Van Camp et al, 1991;Nykjaer and Van Camp, 1994). The development and growth of the larger, permanent filaments seems to be related to changes in topography such as headlands (Strub et al, 1991).…”

Section: Introductionmentioning

confidence: 99%

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Geochemical distribution patterns as indicators for productivity and terrigenous input off NW Africa

Plewa

Meggers

Kuhlmann

et al. 2012

Deep Sea Research Part I: Oceanographic Research Papers

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a b s t r a c tOne hundred and twenty-eight surface-sediment samples collected off North-West Africa were studied geochemically to detect the expressions of different meridional climate regimes and zonal productivity gradients in the surface sediments. This geochemical multi-tracer approach, coupled with additional information on the bulk carbonate and TOC contents makes it possible to characterise the sedimentological regime in detail. Typical terrigenous elements like Al, K and Fe mirror the importance of the humid (fluvial) influence in the north of the study area and the dominance of aeolian input in the south. Furthermore, the distributions of Ti and Fe in the surface sediments serve as tracers for the supply of eolian volcanic material from the Canary Islands. The spatial variability of the TOC contents in the surface sediments closely follows the ocean surface productivity patterns, whereas the CaCO 3 contents are mainly controlled by dilution with terrigenous matter. The potential productivity proxy Ba is not a reliable tracer for productivity in this region, since it is mainly supplied by terrigenous input (coupled with aluminosilicates).

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Geochemical distribution patterns as indicators for productivity and terrigenous input off NW Africa

Plewa

Meggers

Kuhlmann

et al. 2012

Deep Sea Research Part I: Oceanographic Research Papers

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show abstract

“…Although its main impact is in shelf slope waters within ~50-60 km of the coast, its influence extends further offshore. Off Cape Blanc, for instance, giant "filaments" of cool, pigment-rich waters reach several hundred kilometers beyond the shelf break [van Camp et al, 1991;Berthon, 1992]. The upwelling system gives rise to a strong east-to-west decreasing gradient in primary productivity; ~260 g organic C m-2 yr-1 in the mesotrophic region and ~110 g organic C m -2 yr -l in the oligotrophic region [Morel, 1996], with much higher rates in eutrophic coastal waters (~535 g organic C m -2 yr-1 at the Eumeli' eutrophic site; see Figure 1).…”

Section: Regional Settingmentioning

confidence: 99%

Transport of airborne lithogenic material down through the water column in two contrasting regions of the eastern subtropical North Atlantic Ocean

Bory¹,

Newton²

2000

Global Biogeochemical Cycles

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Abstract. Downward particle fluxes were measured using deep-moored sediment traps deployed in two regions of contrasting primary productivity levels (mesotrophic and oligotrophic) of the eastern subtropical North Atlantic Ocean. The high percentage of lithogenic material (~20-30% on average) in the particulate matter collected shows the regional significance of the atmospheric dust inputs originating from West Africa. The magnitudes of lithogenic and biogenic fluxes decrease ~5-6 and -•8-9 fold, respectively, from near the African margin (mesotrophic region) to the remote open ocean (oligotrophic region). These trophic differences seem to give rise to differences in the characteristics of the downward transport of lithogenic material. At the oligotrophic site, the relatively low and slow export of biogenic matter apparently limits and delays the removal of lithogenic particles delivered to surface waters from the atmosphere. In contrast, the higher biological activity in the mesotrophic region seems to provide persistent conditions for an efficient and faster downward transport of the deposited lithogenic particles, and the temporal variability of lithogenic fluxes largely reflects that of the atmospheric dust inputs. Thus whether the temporal variability of the exported lithogenic flux in the water column follows that of the atmospheric deposition appears to depend on the trophic status. In the mesotrophic region the oft-observed linear relationship between lithogenic and particulate organic matter (hereinafter POM) fluxes breaks down at high POM fluxes. This observation adds weight to the idea that linear relationships between POM fluxes and some candidate proxies for POM transfer cannot be assumed when POM export is large. A high mesoscale variability of biogenic, but not lithogenic, fluxes in the water column of the mesotrophic region underscores the relevance of mesoscale studies for regional estimates of export of biogenic material.

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Short‐term upwelling events at the western African coast related to synoptic atmospheric structures as derived from satellite observations

2014

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[1] Satellite scatterometers provide continuously valuable surface wind speed and direction estimates over the global ocean on a regular grid both in space and time. The Level 3 data derived from the Advanced Scatterometer (ASCAT), available at 1/4 spatial resolution (hereafter AS25), and Quick Scatterometer (QuikSCAT), available on 1/2 and 1/4 horizontal grids (QS50 and QS25, respectively), are studied at regional scales in both the Benguela and Canary upwelling systems. They are compared to the European Center for Medium-Range Weather Forecast surface wind analysis, with insight into their intrinsic and actual spatial resolutions. In the coastal band, the finest spatial patterns are found in the QS25 winds and are O(75 km). This demonstrates the sensitivity of the high-resolution satellite-derived winds to coastal processes related to sea surface temperature (SST) perturbations and land-sea transition. Next, short-lived upwelling episodes (SUEs) calculated from SST anomalies are defined consistently with the QS25 actual resolution. These cold events refer to local, short-lived perturbations that add to seasonal upwelling variability. We characterize concomitant atmospheric synoptic conditions for SUEs identified at chosen latitudes and highlight two subregions in both upwelling systems, with contrasted patterns for the alongshore wind stress component and curl. The complexity of the latter patterns is closely linked to local, short-term SST variability. Closer to the shore, numerical sensitivity experiments show that the imbalance between Ekman transport and Ekman pumping has an impact on ocean dynamics: wind reduction in the coastal QS25 forcing, partially induced by orography, tends to reduce coastal SST cooling.

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Upwelling and boundary circulation off Northwest Africa as depicted by infrared and visible satellite observations

Cited by 280 publications

References 17 publications

Geochemical distribution patterns as indicators for productivity and terrigenous input off NW Africa

Geochemical distribution patterns as indicators for productivity and terrigenous input off NW Africa

Transport of airborne lithogenic material down through the water column in two contrasting regions of the eastern subtropical North Atlantic Ocean

Short‐term upwelling events at the western African coast related to synoptic atmospheric structures as derived from satellite observations

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