Upwelling Of Cold Water Research Articles

Interplay of oceanographic and paleoclimate events with tectonism during middle to late Miocene sedimentation across the southwestern USA

Continental sedimentation reflects a complex interplay of tectonics and climate. A 2000-km transect from coastal California to the western Great Plains documents a major increase in sedimentation (ca. 16–6 Ma) coeval with deposition of the hemipelagic Monterey Formation along the California coast. Basin and Range-style regional extension following elongation of the Pacific–North American transform boundary at ca. 17.5 Ma provided fault-bounded basins for accommodation space, but sedimentation also occurred on unextended erosional surfaces of the Great Plains and Colorado Plateau. Two global climate transitions bracket this sedimentary interval. The middle Miocene transition (ca. 17–12 Ma) records the global change from equatorial to meridional circulation caused by: (1) closing of the eastern Tethys Seaway (ca. 18 Ma); (2) opening of the Arctic–North Atlantic connection (ca. 17.5 Ma); (3) growth of the East Antarctic Ice Sheet (ca. 14 Ma); and (4) closing of the Indonesian Seaway (ca. 12 Ma). Upwelling of cold waters along the California coast, abetted by domination of La Nina phases of El Nino–Southern Oscillation (ENSO), progressively aridified the Southwest as reflected in sedimentary and biologic records. The second climate transition occurred as opening of the Gulf of California (ca. 6 Ma) intensified the North American monsoon, resulting in integration of drainages, incision of uplifts, and exhumation of basin fills. The Miocene ended with the driest climate of the Tertiary (both regional and global) accompanied by conversion of savanna to steppe or scrub desert, spread of C4 grasses, and the greatest mammal extinction of the Neogene.

The Role of the Equatorial Currents on the Evolution of SSTA in the Eastern Pacific during Two Different Kinds of El Niño Events

Based on the Simple Ocean Data Assimilation (SODA) from 1970 to 2001, equatorial currents and their association with the warm water propagation mechanism during two patterns of El Nio events are studied. In this study, the middle-pattern of El Nio (ME) and the eastern-pattern of El Nio (EE) events are defined as anomalous warm water originating first to the west and the east of 120°W, respectively. It is pointed out that the westerly and eastward anomalous currents in the western Pacific are stronger during the ME event than the EE event, which is conducive to the eastward migration of warm water from western Pacific by zonal advection of temperature. In contrast, the weaker westerly and the westward anomalous currents east of the dateline would be unfavorable for the eastward migration of warm water during EE events. More importantly, another propagation mechanism of the warm water is attributed to the anomalous convergence of the surface currents, as well as the anomalous divergence of the subsurface currents, which obstruct the upwelling of colder water from the deep ocean. Meanwhile, the anomalous convergence of the surface currents and the anomalous divergence of the subsurface currents maintain eastward migration, which plays an important role in the eastward migration of the warm water during ME events. Although there is anomalous convergence in the upper ocean and anomalous divergence in the subsurface ocean during EE events, they appear quasi-stationary in the western Pacific. The warm water over the eastern Pacific during EE events is caused by the local anomalous convergence of surface currents and the anomalous divergence of subsurface currents.

Numerical Simulation of Air–Sea Coupling during Coastal Upwelling

Abstract Air–sea coupling during coastal upwelling was examined through idealized three-dimensional numerical simulations with a coupled atmosphere–ocean mesoscale model. Geometry, topography, and initial and boundary conditions were chosen to be representative of summertime coastal conditions off the Oregon coast. Over the 72-h simulations, sea surface temperatures were reduced several degrees near the coast by a wind-driven upwelling of cold water that developed within 10–20 km off the coast. In this region, the interaction of the atmospheric boundary layer with the cold upwelled water resulted in the formation of an internal boundary layer below 100-m altitude in the inversion-capped boundary layer and a reduction of the wind stress in the coupled model to half the offshore value. Surface heat fluxes were also modified by the coupling. The simulated modification of the atmospheric boundary layer by ocean upwelling was consistent with recent moored and aircraft observations of the lower atmosphere off the Oregon coast during the upwelling season. For these 72-h simulations, comparisons of coupled and uncoupled model results showed that the coupling caused measurable differences in the upwelling circulation within 20 km off the coast. The coastal Ekman transport divergence was distributed over a wider offshore extent and a thinner ocean surface boundary layer, with consistently smaller offshore and depth-integrated alongshore transport formed in the upwelling region, in the coupled case relative to the uncoupled case. The results indicate that accurate models of coastal upwelling processes can require representations of ocean–atmosphere interactions on short temporal and horizontal scales.

Area utilisation and activity patterns of roman Chrysoblephus laticeps (Sparidae) in a small marine protected area

Information on the movement of fish is vital to determine the effectiveness of marine protected areas (MPAs) for fish conservation and fisheries management. This study investigates area utilisation and activity patterns of 13 adult roman Chrysoblephus laticeps (Sparidae) using telemetry and underwater observations. Acoustic transmitters implanted into C. laticeps in tanks had no apparent effects on growth and mobility. Natural behaviour of the treated fish in the field was verified by SCUBA divers. Manual boat- and diver-based tracking was carried out inside the Castle Rock MPA, False Bay, South Africa, over a 17-month period. A radio acoustic positioning system (VRAP, VEMCO Ltd) was used to record automatically fish positions over two 1-month periods during and after the spawning season of roman. Manually recorded fish positions and VRAP positions inside the triangle of buoys within the system were accurate within 10m; deviations increased with increased distance of the fish from the centre of the system and during unfavourable sea conditions. Analysis of movement data using a 95% fixed kernel algorithm suggests that roman occupy small home ranges of between 1 000m2 and 3 000m2, which shows that this species is well suited for protection in small MPAs. Interestingly, the home range size did not seem to be related to fish size or habitat quality. Swimming activity decreased at night. During periods of cold-water upwelling, fish retreated into caves. During the spawning season, females extended their home ranges, which result in a 'spill over' effect of adult fish into fishing areas.

Oligocene to Holocene glauconite–phosphorite grains from the Head of the Cape Canyon on the western margin of South Africa

Abstract Glauconite and carbonate–fluorapatite (CFA) are significant components of the condensed Upper Oligocene to Holocene sediment succession recovered from the western margin of southern Africa. The detailed texture and geochemistry of these glauconite–phosphorite grains are reported here within the stratigraphic framework established on the outer continental shelf in the Head of the Cape Canyon area. Three texturally and stratigraphically distinct glauconite grain types are recognised: Oligo/Miocene infilled foraminiferal tests, Mio/Pliocene green and Quaternary dark green to black grains. Most of these glauconitic grains include a minor to significant amount of CFA. The Upper Oligocene to Lower Miocene sediment succession is dominated by fine sand-sized benthic and planktic foraminifera. Glauconite grains constitute 20–50% of the sediment and represent tests infilled by variable proportions of glauconite and CFA cement with the test wall replaced by CFA only. Glauconite–CFA formation during the Late Oligocene to Early Miocene was associated with warm-water upwelling coupled with third-order marine transgressions. Rare-earth element (REE) chemistry indicates that sub-oxic conditions prevailed during diagenesis. Mio/Pliocene green and Quaternary dark green to black medium sand-sized glauconite grains constitute between 20% and 95% of these predominantly siliciclastic sediments. The green to black glauconite grains are texturally different, but have similar major and REE chemistry. Since the mid-Miocene, formation of glauconite–CFA grains is associated with cold-water upwelling and detrital, Fe-rich terrigenous mud deposition in oxic to suboxic bottom waters analogous to the Holocene coast-parallel, organic-rich mudbelt on the shelf. The texture of these grains indicates repeated cycles of glauconite and CFA authigenesis during marine transgressions and winnowing and reworking during marine regressions.

Sea surface temperatures of the western Arabian Sea during the last deglaciation

In this study we present a sea surface temperature (SST) record from the western Arabian Sea for the last 20,000 years. We produced centennial‐scale δ18O and Mg/Ca SST time series of core NIOP929 with focus on the glacial‐interglacial transition. The western Arabian Sea is influenced by the seasonal NE and SW monsoon wind systems. Lowest SSTs occur during the SW monsoon season because of upwelling of cold water, and highest SSTs can be found in the low‐productivity intermonsoon season. The Mg/Ca‐based temperature record reflects the integrated SST of the SW and NE monsoon seasons. The results show a glacial‐interglacial SST difference of ∼2°C, which is corroborated by findings from other Arabian Sea cores. At 19 ka B.P. a yet undescribed warm event of several hundred years duration is found, which is also reflected in the δ18O record. A second centennial‐scale high SST/low δ18O event is observed at 17 ka B.P. This event forms the onset of the stepwise yet persistent trend toward Holocene temperatures. Highest Mg/Ca‐derived SSTs in the NIOP929 record occurred between 13 and 10 ka B.P. Interglacial SST is ∼24°C, indicating influence of upwelling. The onset of Arabian Sea warming occurs when the North Atlantic is experiencing minimum temperatures. The rapid temperature variations at 19, 17, and 13 ka B.P. are difficult to explain with monsoon changes alone and are most likely also linked to regional hydrographic changes, such as trade wind induced variations in warm water advection.

Sea surface temperatures during the SW and NE monsoon seasons in the western Arabian Sea over the past 20,000 years

The western Arabian Sea is influenced by the seasonal southwest and northeast monsoon wind systems. In the modern day, SW monsoon induced upwelling of cold water leads to lowest SSTs in summer, while in glacial periods, weakened upwelling and increased cooling by NE monsoon winds may have resulted in lowest SST in winter. In order to reconstruct the western Arabian Sea seasonal sea surface temperature (SST) evolution during the monsoons over the past 20,000 years, a novel proxy is used that captures the contrast in seasonal SSTs. The presented proxy concerns the difference in δ 18O between two shallow dwelling species of planktonic foraminifera; Globigerinoides ruber, which calcifies throughout the year, and Globigerina bulloides, which mainly calcifies during SW monsoon driven upwelling. We convert this δ 18O difference to the difference in calcification temperature (ΔTc rub − bul), and use it in combination with Mg/Ca-derived temperatures to reconstruct seasonal SSTs. We present the monsoon evolution record of Core NIOP929, located NW of the island of Socotra. Based on our results we distinguish three distinct modes. I) A glacial monsoon mode (20–13 ka BP) characterised by weakly negative ΔTc rub − bul values, and SW monsoon SSTs ( T SW) that are ∼ 2 °C higher than NE monsoon SSTs ( T NE). This pattern is indicative for a weak SW monsoon and stronger cooling by glacial NE monsoon winds compared to the modern situation. II) A transitional mode (13–8 ka BP) characterised by ΔTc rub −bul values around 0, and thus a reduced difference between T SW and T NE. III) The modern monsoon mode, which started at 8 ka BP with the main shift toward low summer SSTs and high winter SSTs. The modern mode is characterised by ΔTc rub − bul values around + 4 °C, indicative of a strong SW monsoon associated with strong upwelling, and weak influence of the NE monsoon on SST. We propose that measuring Mg/Ca on both species will improve the accuracy of the SST estimates.

Spatial distribution of phytoplankton <13μm in the Gulf of Cádiz in relation to water masses and circulation pattern under westerly and easterly wind regimes

Spatial distribution of both abundance and biomass of phytoplankton o13mm were analysed by flow cytometry, distinguishing eukaryotic picoplankton, nanoplankton, cryptomonads, Synechococcus and Prochlorococcus. These groups were related to different circulation patterns observed in two successive mesoscale samplings in the Gulf of Cadiz. The first sampling was characterized by westerly-driven upwelling processes around Cape Santa Maria and a surface signal of the Huelva front. During the second sampling easterlies blew and warm waters covered the shelf between Cadiz and Cape Santa Maria although a reminiscent upwelling was still observed west of the cape. Under the first wind regime, lowest phytoplankton abundance was measured in the upwelling area probably due to time lag of phytoplankton response, whereas the highest abundance occurred associated with the Huelva front (T� 161C). During the second cruise and under easterly wind regime, higher phytoplankton abundance and biomass of all groups were found as compared to the first period. Phytoplankton accumulation was mainly associated with the 161C isotherm in upwelled waters and in warm shelf waters. In the mixing area between warm shelf waters and cold upwelled waters, phytoplankton size spectra were found to be less negative in the warm stratified side than in the cold mixed side. This unusual feature was attributed to the warming and nutrient enrichment of shelf water during each tidal cycle in river delta and marshes located around the Gulf of Cadiz, leading to elevated biomass around these structures. On TS diagrams, eukaryotic nanoplankton was associated with warm shelf water, eukaryotic picoplankton and Synechococcus with upwelled water, while Prochlorococcus reached highest abundances in deeper water (50-75 m) associated with the mixing line between North Atlantic Central Water and Surface Atlantic Water. r 2006 Elsevier Ltd. All rights reserved.

Late Cenozoic evolution of the outer continental shelf at the head of the Cape Canyon, South Africa

Cenozoic sedimentary successions have a restricted distribution, both onshore and offshore, along the passive western margin of southern Africa and much controversy and uncertainty remains on the geological evolution of this margin. Siliciclastic, authigenic and biogenic sediments, varying in age from Cretaceous to Holocene, recovered from a number of vibrocores collected between 200 and 500 m water depth, at the head of the Cape Canyon, provide the basis for an integrated bio-, Sr-isotopic and lithostratigraphic study. The study area is underlain by unconsolidated middle Cretaceous interbedded woody quartzose sand and kaolinitic mud. A large regional erosional hiatus separates the upper Oligocene to lower Miocene carbonate sediments from these Cretaceous sediments. The upper Oligocene to lower Miocene (18.1–27.2 Ma) carbonate succession records third-order sea-level fluctuations superimposed on an overall marine transgression. The interpreted late Oligocene depositional environments imply increased bottom-water activity over time and the peak in phosphogenesis at 23.6–26.1 Ma indicates the onset of warm-water upwelling. Calcareous deposition ended at around 18 Ma when downwarping of the continental shelf associated with uplift of the continental interior resulted in the seaward tilt of the carbonate succession to greater water depths. Increased terrigenous input is recorded as inner shelf prograding quartzose delta-front deposits following uplift of the interior. Uplift combined with a long-term marine regression resulted in the widespread erosion of middle to upper Miocene successions, generally recovered only as reworked glauconite–carbonate fluorapatite (CFA) mixed mineral pellets above the erosional hiatus. Glauconite-rich sediments indicate overall low accumulation rates and multiple reworking events of organic-rich clayey sediments during the middle to late Miocene/early Pliocene. Onset of cold-water upwelling, at least intermittently by ± 15 Ma, established hydrographic conditions similar to the Benguela Upwelling System with a coast-parallel mudbelt present on the middle shelf. A middle Pliocene marine regression reworked 15.8–9.1 Ma inner shelf quartzose delta-front sediments across the outer shelf. Late Pliocene/early Pleistocene uplift of the continental interior resulted in the fault-controlled incision of the head of the Cape Canyon along the seaward flank of the buoyant Agulhas–Columbine basement block. Uplift increased Quaternary terrigenous sedimentation on the shelf, where the facies distribution was clearly controlled by Canyon head bathymetry. High-frequency glacio-eustatic sea-level fluctuations resulted in late Quaternary erosion and slumping across the outer shelf and the continued downcutting of the Cape Canyon. Lowstand shelly gravels are common, including the Last Glacial Maximum shell lag, which grades into a faecal pellet rich Holocene mud drape over much of the study area. The late Cenozoic evolution of the western margin recorded in the complex condensed sediment record of the study area is characterised by low sediment accumulation rates and multiple reworking events. The integrated stratigraphic interpretation emphasises the importance of eustasy, tectonic activity, fluvial sediment input, palaeoceanographic and climatic changes.

Wintering seabirds in West Africa: foraging hotspots off Western Sahara and Mauritania driven by upwelling and fisheries

Cold-water upwelling supports abundant and diverse faunas. Upwelling off Mauritania has been highlighted as being important for seabirds, but very few systematic offshore surveys have been conducted in that region. Mauritanian waters are increasingly targeted by commercial fisheries along the shelf break and, with the likelihood of future exploitation of mineral oils on the continental shelf, the absence of information on seabirds is worrying. This paper describes the distribution of wintering seabirds in the context of fisheries and hydrography. The avifauna was dominated by surface-feeding and shallow plunge-diving, often planktivorous, seabirds, originating from West Palaearctic breeding grounds (Arctic, subarctic and temperate zones). Many seabirds were associated with fishing trawlers around the shelf break, but the fleets were more evenly distributed than the birds, with certain hydrographical parameters influencing or overruling the attraction of trawlers by seabirds. The results support the belief that West African waters are of prime importance for seabirds.

What's happening in Monterey Bay on seasonal to interdecadal time scales

Daily observations of sea-surface temperature (SST) have been acquired at the southern end of Monterey Bay in Pacific Grove, California since 1919. It is one of the longest oceanographic records off the west coast of North America. The record is examined to determine the major sources of variability in Monterey Bay and beyond, on time scales from seasonal to interdecadal. On seasonal time scales, the spring transition to coastal upwelling, often a major event along the coast of central California, is not well-expressed inside the bay but is detectable, occurring, on average, between mid-March and mid-April. The onset of the Davidson Current in Monterey Bay is well-defined, occurring, on average, in mid-October, ±2–3 weeks. Intraseasonal changes also occur during the spring and summer that may correspond to intrusions of warmer offshore waters into Monterey Bay. Intraseasonal oscillations with periods in the range of 40–50 days occur in Monterey Bay, but compared to their signature along the open coast, their event-like behavior is modified. The annual cycle of surface temperature in Monterey Bay is asymmetric with seasonal warming occurring during the spring and summer, and cooling during the fall. This asymmetry is primarily due to the net surface heat exchange which is positive for most of the year, and, to a lesser extent, the influence cold upwelled waters that are advected into the bay during the spring and summer, observations supported by a simple model that combines both the net surface heat exchange and thermal advection. On interannual time scales, the influence of El Niño warming events is strong. A comparison with the Northern Oscillation Index (NOI) using Singular Spectrum Analysis (SSA), shows that the El Niño signal is often as strong in SST at Pacific Grove as it is in the NOI. On interdecadal time scales, the influence of the Pacific Decadal Oscillation (PDO) is also relatively strong in Monterey Bay, again based on SSA. The integrated anomaly was calculated from the record and reveals regime shifts in Monterey Bay that occurred in 1929, an event that was apparently regional in scale, reflecting a transition from unusually cold to warmer conditions, and the regime change in the PDO that occurred in 1976. Each regime change can be approximated by a step-wise increase in temperature. Finally, linear trends were estimated for the entire record (∼+0.01 °C/year), and for the 72-year period from 1930 to 2001 (+0.0042 °C/year), i.e., following the regional regime change in 1929. The estimated trend for the last 72 years is not statistically significant; however, it is in close agreement with the long-term trend for the Intergovernmental Panel on Climate Change (IPCC) record of global surface temperature that spans almost 140 years (∼+0.005 °C/year). Although the long-term increase in SST at Pacific Grove appears to be consistent with global warming, the integrated anomaly suggests that temperature increases in Monterey Bay have occurred rather abruptly and thus it becomes more difficult to invoke the global warming scenario. Finally, based on the monthly averaged data, the annual cycle, El Niño warming episodes, the PDO, the long-term trend, and the semiannual cycle account for approximately 44%, 18%, 6%, 4%, and 3% of the total variance, respectively, in SST at Pacific Grove.

Energy storage and utilization in relation to the reproductive cycle in the razor clam Ensis arcuatus (Jeffreys, 1865)

AbstractSeasonal changes in condition indices and biochemical components of the digestive gland, anterior adductor muscle, foot, and gonad of Ensis arcuatus (Jeffreys, 1865) were analysed from February 1998 to June 1999 in relation to environmental conditions and reproductive events. During summer, E. arcuatus accumulated lipids, particularly triacylglycerols, in the digestive gland and glycogen in the anterior adductor muscle and foot while the gonad was in sexual rest. Phytoplankton blooms caused by the upwelling of cold waters, rich in nutrients, from offshore are responsible for the high availability of food during reserve storage. In autumn, when gametogenesis started, oceanographic conditions changed to a situation with low temperature throughout the water column because of the vertical mixing, and food became scarce. At that point in time, the energy requirements for basal metabolism and the reproductive process were provided by the mobilization of triacylglycerols and glycogen stored in the digestive gland and muscle tissues, respectively. The pattern exhibited by E. arcuatus based on the accumulation of reserves in summer and the subsequent mobilization during gonadal development seems to follow a conservative pattern.

Summer exchange between Hamilton Harbour and Lake Ontario

A field study conducted in the summer of 1996 investigated exchange flow between Hamilton Harbour and Lake Ontario through the Burlington Ship Canal. Prevailing westerly winds during July caused upwelling of cold water in Western Lake Ontario. A two-layer exchange flow through the canal was driven by the resulting density difference between Lake Ontario and Hamilton Harbour. In the canal, a lower layer of cold lake water flowed into the harbour while an upper layer of warm harbour water flowed out into Lake Ontario. The intrusion of fresh, cool, oxygenated Lake Ontario water had a dramatic impact on the hypolimnion of Hamilton Harbour. When the prevailing winds shifted to the east in early August downwelling in Western Lake Ontario resulted in a reduced exchange flux that included an episode of ‘reverse’ exchange with an upper layer of warmer lake water flowing into the harbour. The volume of the exchange during July 8–28 was estimated to be 23% of the harbour volume, with daily mean exchange fluxes of 25–50 m3/s. During sustained upwelling, July 16–28, the exchange was 54% less than predicted by inviscid two-layer hydraulics. Frictional effects accounted for 45% of this reduction, while recirculation due to interfacial mixing accounted for the remaining 9%.

Summer exchange between Hamilton Harbour and Lake Ontario

Abstract A field study conducted in the summer of 1996 investigated exchange flow between Hamilton Harbour and Lake Ontario through the Burlington Ship Canal. Prevailing westerly winds during July caused upwelling of cold water in Western Lake Ontario. A two-layer exchange flow through the canal was driven by the resulting density difference between Lake Ontario and Hamilton Harbour. In the canal, a lower layer of cold lake water flowed into the harbour while an upper layer of warm harbour water flowed out into Lake Ontario. The intrusion of fresh, cool, oxygenated Lake Ontario water had a dramatic impact on the hypolimnion of Hamilton Harbour. When the prevailing winds shifted to the east in early August downwelling in Western Lake Ontario resulted in a reduced exchange flux that included an episode of ‘reverse’ exchange with an upper layer of warmer lake water flowing into the harbour. The volume of the exchange during July 8–28 was estimated to be 23% of the harbour volume, with daily mean exchange fluxes of 25–50 m3/s. During sustained upwelling, July 16–28, the exchange was 54% less than predicted by inviscid two-layer hydraulics. Frictional effects accounted for 45% of this reduction, while recirculation due to interfacial mixing accounted for the remaining 9%.

SPATIAL AND TEMPORAL VARIABILITY OF THERMAL FRONTS OFF CENTRAL CHILE (33-40S)

During the upwelling season along the coast off central Chile (33-40S), cold upwelled water can be easily distinguished from warm oceanic water using satellite infrared images. The boundary between cold and warm surface waters is a relatively narrow region with large horizontal gradients, denominated upwelling front, which is also clearly visible in satellite images. Here, using daily NOAA satellite infrared images from the period 1998-2000, we described the spatial distribution of mesoscale features related to upwelling fronts. Together with infrared data, we use SeaWiFS's color images to explore the relationship between Chlorophyll concentration and thermal upwelling fronts. Our results show that thermal fronts have maximum intensities (0.2C/km) in spring and summer and they are typically located between 30 and 300 km off the coast. The offshore extension of the upwelling front was usually larger between 35-37S, related to the presence of a large anticyclonic eddy in this region during the warm season. In general, chlorophyll was well correlated (inversely) to SST showing similar offshore variability scale and covariance in mesoscale features like eddies and filaments

Climatology and Variability of Sea Surface Temperature and Surface Chlorophyll in the Benguela and Agulhas Ecosystems As Observed by Satellite Imagery

A climatology of satellite-derived sea surface semperature (SST) and surface chlorophyll a concentration (Chl), and their associated variability at time-scales from weeks to years, was constructed for the Benguela and Agulhas ecosystems. Global area coverage data at 4.5 km spatial resolution from both AVHRR and SeaWiFS sensors were used to assemble the climatology, from weekly and 5-day time-series respectively. The SST data series spanned 18 years (1982–1999), the Chl data the period September 1997–April 2002. The dominant pattern in the annual SST is the cold upwelled water on the western continental shelf of South Africa and Namibia. SST was high at the Angola-Benguela Front (15–17°S) and on the Agulhas Bank, the northern and southern extremities of the upwelling region. Monthly SST variability was high in both regions, except for the Lüderitz and Cape Columbine-Cape Peninsula upwelling zones, where variability was low. The western Agulhas Bank exhibited a clear seasonal pattern of warm surface water in summer and cool surface water in winter, with an amplitude of 2.5°C. A band of high Chl (>5–10 mg m−3) was apparent close to the coast from the Angola-Benguela Front to Cape Town, but there was a well-defined relative minimum at Lüderitz. On the South Coast, highest Chl (>3 mg m−3) was between Cape Agulhas and Port Elizabeth, in the form of a plume moving offshore. In contrast to SST, Chl variability was mainly at intramonthly intervals, although variability was particularly high north of the Angola-Benguela Front in summer, and at various upwelling sites in winter.

Widespread, prolonged late Middle to Late Ordovician upwelling in North America: A proxy record of glaciation?: Comment and Reply

[Pope and Steffen (2003)][1] described an interesting new model suggesting relations between the Gondwana glaciation and late Middle (Chatfieldian) through Late Ordovician (Cincinnatian) upwelling of cold water and chert formation. They used the distribution of Middle and Late Ordovician chert-

Evolución de un evento de surgencia frente a punta Curaumilla, Valparaíso

The beginning, maturity and relaxation phases of a coastal upwelling event (16 to 20 January 1986), off punta Curaumilla (33°06'S), were characterized. This characterization was based on the spatial and time distribution of temperature, salinity, dissolved oxygen, nutrients (nitrate, phosphate and silicate), wind and Ekman transport. Satellite images of sea surface temperature were used as complementary information. The results showed that the winds were fluctuating and mainly blowing from the south and southwest, so it was possible to observe the initial and mature phases and the beginning of the relaxation phase. The initial phase was characterized by an increase of the south and southwest wind and the Ekman transport, a rise of the seasonal thermocline at the coast and the presence of a cold surface water plume 45-55o towards the left of the coastline. The mature phase was characterized by the presence of strong winds (>10 m·s -1 ), high mean Ekman transport (>1,000 m 3 ·s -1 per 1,000 m of coast), a lowering of the temperature ( 34.4 psu) and nutrients (phosphate >2.0 µM; nitrate >15 µM; silicate >10 µM ) at the coastal margin. The declination phase was partially observed, because the wind did not relax enough during the sampling period. However, the surface temperature satellite images on 23 and 24 January, clearly showed a decrease of the area covered with cold upwelled water. The water mass displaced towards the ocean had Subantarctic characteristics and the water mass upwelled to the surface, had Equatorial Subsurface characteristics.

Identifying characteristic chlorophyll a profiles in the coastal domain using an artificial neural network

To estimate primary production in the marine environment, knowledge of the vertical distribution of phytoplankton is needed. The measurement of ocean colour by satellite remote sensing makes it possible to map the near-surface phytoplankton distribution, although the subsurface vertical structure cannot be measured. In this study, we investigated the shape of vertical chlorophyll profiles from the Benguela upwelling system seasonally and with respect to environmental variables such as surface temperature and chlorophyll, and mixed layer and water column depth. We used an artificial neural network technique called a self-organizing map to identify characteristic classes of vertical chlorophyll profiles, and then classify existing profiles into these representative classes. The self-organizing map identified a continuum of patterns, ranging from those with small deep peaks (1 mg m(-3), 45 m) to those with large near-surface peaks (9 mg m(-3), 7 m). Although profile shape varied seasonally, profiles were very variable within each season, making chlorophyll profiles averaged seasonally meaningless. A canonical succession in profile shape following upwelling of cold water in spring and summer could be identified, with large surface peaks in cool water and small deep peaks in warm water. The approach presented here can be used in a semi-quantitative manner to predict the subsurface chlorophyll field from known (water column depth) or easily measured variables from satellites (surface temperature or surface chlorophyll), as the relative frequency of each characteristic profile under different environmental conditions is presented. This approach enables prediction of profile shapes in the dynamic coastal domain and thus superior regional estimates of primary production.

The relationship between the North American summer monsoon, the Rocky Mountains and the North Pacific subtropical anticyclone in HadAM3

AbstractIn this study the relationship between the North American monsoon, the Californian sea surface temperature (SST) cold pool, the Rocky Mountains and the North Pacific subtropical anticyclone is investigated using the Hadley Centre's atmospheric climate model, HadAM3. In 1996 Hoskins hypothesized that heating in the North American monsoon might be important for the maintenance of the summertime North Pacific subtropical anticyclone, since the monsoon heating may induce descent to the north‐west of the monsoon in the descending eastern flank of the subtropical anticyclone. This descent is further enhanced by radiative cooling and is associated with equatorward surface winds parallel to the western coast of North America. These equatorward winds induce oceanic upwelling of cold water and contribute to the formation of the Californian SST cold pool, which may feed back on the anticyclone by further suppressing convection and inducing descent. More recently, Rodwell and Hoskins also investigated the global summer monsoon–subtropical anticyclone relationship. They examined the role that mountains play in impeding the progress of the low‐level mid‐latitude westerlies, either deflecting the westerlies northwards where they ascend along the sloping mid‐latitude isentropes or deflecting them southwards forcing them to descend along the isentropes. In particular, the introduction of the Rockies into a primitive‐equation model adiabatically induces descent in the eastern descending flank of the North Pacific subtropical anticyclone.These hypothesized mechanisms have been investigated using HadAM3, focusing on the possible suppression of convection by the Californian SST cold pool, the response of the North Pacific subtropical anticyclone to the strength of the North American monsoon and the ‘blocking’ of the mid‐latitude westerlies by the Rocky Mountains. The role of the Rockies is examined by integrating the model with modified orography for the Rocky Mountains. Changing the height of the Rockies alters the circulation in a way consistent with the mechanism outlined above. Higher Rocky mountains force the westerlies southwards, inducing descent in the eastern flank of the subtropical anticyclone as the air descends along the sloping isentropes.The relationship between the North American monsoon and the North Pacific subtropical anticyclone is investigated by suppressing the monsoon in HadAM3. The suppression of the monsoon is accomplished by increasing the surface albedo over Mexico, which induces anomalous ascent on the eastward flank of the subtropical anticyclone and anomalous polewards surface winds along the western coast of the North American continent, also providing support for the above hypothesis. The removal of the Californian SST cold pool, however, has a statistically insignificant effect on the model, suggesting that in this model the feedback of the SST cold pool on the eastern flank of the anticyclone is weak. Copyright © 2002 Royal Meteorological Society.