Search

We predicted small-scale hydrodynamics, including the effect of the aquaculture farming infrastructure, for a region within the group of salmon farm concessions identified in the Chilean regulation as ACS-7. The geographical region corresponds to the Caucahue Channel, composed of two branches connected by a constriction on Caucahue Island, Inland Sea of Chiloe, Chilean Patagonia. The prediction methodology considers the interaction of a regional ocean model and a high-resolution local CFD model. The model prediction was validated using available data from ADCP. We find that the Caucahue Channel is characterized by a complex circulation and hydrodynamics, including an unstable shear flow, with meanders and turbulent structures, and retention zones. Results show the aquaculture infrastructure has a non-local hydrodynamic effect. Differences in horizontal and vertical velocity can be quite significant even far from aquaculture centers, reaching up to 300% and 170%, respectively, in simulations without taking its effects into account. The useful characteristics of this predictive approach and its potential use in particle tracking and species diffusion prediction allow for the use of projecting as a tool for strengthening the environmental and productive management of this industry.

Some bays of the subtropical west coast of South America, usually protected from the winds, have been observed as upwelling shadows (US), with anomalous high sea surface temperatures. Different arg...

Climatological hydrographic data for the southeastern Pacific from the World Ocean Atlas show an extended low-salinity region associated with high rainfall/river runoff along the Chilean Patagonia coast. However, the structure and variability of this extensive freshwater area is poorly understood due to the lack of periodic hydrographic observations. Here, we use 15 years of satellite observations in combination with hydrographic data from Argo profiling floats to increase our understanding of the freshwater structure and its seasonal variability off western Patagonia. Satellite-derived seasonal fields of surface salinity from Aquarius/SAC-D and SMAP (Soil Moisture Active Passive) satellite missions reveal a prominent coastal band of low-salinity water year-round (fresher during spring and summer). Hydrographic profiles from Argo floats confirm this coastal freshening. The major content of freshwater is located off central Patagonia, where the low-salinity surface layer dominates the stratification of the upper ocean. In contrast, the freshwater content plays a minor role in setting up the stratification off northern and southern Patagonia. A warm surface layer greatly increases the stability of the upper 500 m in the northern sector (especially in summer and fall), whereas cold temperatures in the southern region tend to damp zonal density gradients and decrease the stratification. Future studies at interannual scales are suggested considering the melting of Patagonian icefields since the 1960s.

Ongoing global warming caused by climate change has been suggested to produce an intensification of upwelling-favorable winds along the coast of south-central Chile due to a poleward displacement of the South Pacific Anticyclone (SPA). Here we explore the extent to which these changes have influenced water column properties, inorganic nutrients, primary production, diatom abundances and net community metabolism (GPP/CR) in these shelf waters. Our analysis is based on a monthly time series (2003–2013) of in situ oceanographic and biological observations and experiments to assess gross primary production (GPP) and community respiration (CR) at a shelf station in central Chile (∼36.5°S), along with ancillary data on alongshore wind variability, river outflow and MODIS-derived surface fluorescence (nFLH). A reduction in river outflow from 2007 onwards, forced remotely by the poleward displacement of the SPA, resulted in a cooler and saltier water column, with lower dissolved Si:N ratios (Si(OH)4: NO3−) and net community metabolism shifting from high net autotrophy (mean GPP/CR = 10.9 ± 14) to a balance between production and respiration (GPP/CR = 1.17 ± 0.6). A key finding was that most of the observed inter-annual variability in diatom abundance and primary production rates from 2003 to 2013 could be explained by two opposite trends: a significant intensification of upwelling-favorable winds during early spring (October-November) post-2009, and a sustained drop in freshwater discharged by the main local river during the same period. A combination of more intense equatorward winds and weaker stratification of the water column may have driven mixing and turbulence beyond the levels that are suitable for diatom growth when the upwelling period began (October-November), and subsequently may have enhanced the offshore transport of nutrients and productivity during late summer months (February-March). Patterns revealed by the analysis of monthly composites of normalized surface fluorescence (nFLH) are consistent with this interpretation. Further intensification of upwelling-favorable winds, combined with changes in the pattern of precipitation and river discharges, may have negative effects on the composition, productivity, and carbon export in shelf waters of this and other coastal upwelling ecosystems.

Residual circulation from nonlinear interaction of the tidal currents with topography in channels, fjords and bays can be important to represent the distance traveled by suspended materials in the water column (e.g. pathogens). Here the role of the semidiurnal tidal excursion was compared with residual currents, during autumn 2011, to evaluate the connectivity among aquaculture production centers in Caucahue Channel (Chiloe Island, southern Chile), which has been widely occupied by the aquaculture industry. During 2015, around 30000 t of 3 different species of salmon were harvested in this channel, representing 3.7% of the national production. Along- and cross-channel tidal currents explained around 80 and 40-60% of the total variance, respectively. Thus, the major residual circulation came from the cross-channel component (40-60% of the total variance) caused by tidal asymmetry. We hypothesized that this asymmetry is related to the nonlinear interaction of the oscillatory flow with the Quemchi constriction. The residual advective distances (Ladv) were compared with tidal excursion (Lexc) and biological diffusivity (Ldiff) scales, considering the distances between centers (Lint), the size of the centers (Lcen) and the length of the south arm of the Cauchaue Channel (L = 11 km). For 3 d time scales, the Ladv/Lexc ratio fluctuated between 1.3 and 8, approximately, implying that, although the advective scale is greater, the tidal flow is still intense enough to favor the retention of pathogens. For larger time scales that consider longer-lived pathogens (e.g. greater than 15 d), this ratio grows 1 order of magnitude. In this scenario and in the event of an outbreak within the channel, pathogens could be exported.

Chromophoric dissolved organic matter (CDOM) is a biologically active component of dissolved organic matter that influences the optical properties of aquatic environments, thereby playing an important role in the photochemical and photobiology processes occurring in the euphotic layer. Three cruises were carried out at three contrasting oceanographic areas off central and southern Chile (36.8°S, 44.6°S, 54.9°S) between November 2013 and July 2017 in order to assess the variability of the CDOM pool's optical properties (a325, SCDOM, SR). Marked differences, including vertical variability, were found for a325, SCDOM, and SR within and among each of the three zones, although surface DOC concentrations remained constant at all sites (87.59 ± 26.04 µmol L−1). At the coastal area close to the Biobio River (36.8°S), a325 values varied between 0.26–1.93 m−1 with maximum measured in surface waters. For the Puyuhuapi fjord in northern Patagonia (44.6°S), a325 ranged between 0.69 and 3.86 m−1, while in the Beagle Channel (54.9°S) it oscillated between 0.59 and 1.73 m−1. We identified the terrestrial organic matter input to surface waters as the main factor influencing surface CDOM concentrations in central Chile. In the Puyuhuapi fjord, terrestrial influence was heterogeneous because of its seasonal variability of the Channel but it was overall less significant than in situ produced CDOM. We also observed the lowest contribution of terrestrial CDOM inputs compared to the in situ production in southern Patagonia (Beagle Channel). We observed that the distribution of CDOM is potentially dominated by biological in situ production below the surface freshwater-influenced layer in the southern area while highly influenced by terrestrial input in the coastal upwelling area at 36°S. Overall, this study shows that the optical properties of dissolved organic matter (mainly SR) can be suitable for identifying different CDOM pools in coastal areas of contrasting oceanographic conditions. In stratified systems, freshwater inputs determine the distribution of surface CDOM while in well-mixed conditions, the in situ production determine the general CDOM concentration.

Ocean color imagery from MODIS (Moderate Resolution Imaging Spectroradiometer) onboard the Aqua platform is used to characterize the interannual variability of turbid river plumes off central-southern Chile. Emphasis is placed on the influence of climate fluctuations, namely El Nino Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Antarctic Oscillation (AAO). Additional satellite data on wind, boat-based hydrographic profiles, and regional climate indices are used to identify the influence of climate variability on the generation of anomalous turbid river plumes. The evolution of salinity at a coastal station on the 90 m isobath between the Itata and Biobio Rivers shows a freshwater surface layer with salinity 32.5 and 5–10 m thick during major plume events in 2002, 2005 and 2006. Surface salinity minima are correlated with peaks in turbidy from the normalized water leaving radiance at 555 nm (nLw(555)), both representing turbid river plumes. EOF analysis reveals that major turbid plume events occurred primarily during warm phases of the ENSO and PDO, and negative phases of the AAO, when storm tracks are further north. Anomalously large turbid plumes extend long distances offshore ( ∼ 70–80 km), and individual plumes coalesce into a continuous plume along the coast that covers the entire continental shelf. Season-specific correlation analyses reveal an increased influence of the AAO on river plumes south of Punta Lavapie in spring-summer (negative correlation). North of this major cape, ENSO and PDO indices have a dominant influence on plumes with positive correlations with the nLw(555) signal in winter (and negative in summer). We discuss the biogeochemical implications of plume events and the importance of long-term and high-resolution ocean color observations for studying the temporal evolution of river plumes.

Submarine canyons cutting across the continental shelf can modulate the cross-shelf circulation being effective pathways to bring water from the deep ocean onto the shelf. Here, we use 69 days of moored array observations of temperature and ocean currents collected during the spring of 2013 and winter-spring 2014, as well as shipboard hydrographic surveys and sea-level observations to characterize cold, oxygen poor, and nutrient-rich upwelling events along the Biobio Submarine Canyon (BbC). The BbC is located within the Gulf of Arauco at 36° 50'S in the Central Chilean Coast. The majority of subtidal temperature at 150 m depth is explained by subtidal variability in alongshore currents on the canyon with a lag of less than a day (r2 = 0.65). Using the vertical displacement of the 10° and 10.5°C isotherms, we identified nine upwelling events, lasting between 20 h to 4.5 days, that resulted in vertical isothermal displacements ranging from 29 to 137 m. The upwelled water likely originated below 200 m. Majority of the cooling events were related with strong northward (opposite Kelvin wave propagation) flow and low pressure at the coast. Most of these low pressure events occur during relatively weak local wind forcing conditions, and were instead related with Coastal Trapped Waves (CTWs) propagating southwards from lower latitudes. These cold, high-nutrient, low-oxygen waters may be further upwelled and advected into the Gulf of Arauco by wind forcing. Thus, canyon upwelling may be a key driver of biological productivity and oxygen conditions in this Gulf.

A combined data set, combining data from field campaigns and oceanographic cruises, was used to ascertain the influence of both river discharges and upwelling processes, covering spatial and temporal variation in dissolved inorganic carbon (DIC) and aragonite saturation state. This work was conducted in one of the most productive river-influenced upwelling areas in the South Pacific coasts (36°S). Additionally, further work was also conducted to ascertain the contribution of different DIC sources, influencing the dynamics of DIC along the land-ocean range. Six sampling campaigns were conducted across seven stations at the Biobio River basin, covering approximately 200 km. Three research cruises were undertaken simultaneously, covering the adjacent continental shelf, including 12 sampling stations for hydrographic measurements. Additionally, six stations were also sampled for chemical analyses, covering summer, winter, and spring conditions over 2010 and 2011. Our results evidenced that seaward extent of the river plume was more evident during the winter field campaign, when highest riverine DIC fluxes were observed. The carbonate system along the river-ocean continuum was very heterogeneous varying over spatial and temporal scales. High DIC and pCO2 were observed in river areas with larger anthropogenic effects. CO2 supersaturation at the river plume was observed during all campaigns due to the influence of low pH river waters in winter/spring and high-pCO2 upwelling waters in summer. δ13CDIC evidenced that main DIC sources along the river and river plume corresponded to the respiration of terrestrial organic matter. We have linked this natural process to the carbonate saturation on the adjacent river-influenced coastal area, suggesting that Ωaragonite undersaturation in surface/subsurface waters is largely modulated by the influence of both river discharge and coastal upwelling events in this productive coastal area. Conditions of low Ωaragonite might impact negatively physiological traits for marine organisms, such as bivalves, gastropods, and crustaceans. Therefore, local populations from river-influenced sites could be inherently more tolerant to ocean acidification than organisms living in regions with lower Ωaragonite variability.

At 03:34 (local time) on 27 February 2010, the world's sixth largest earthquake on record (8.8 Mw) occurred off central Chile, rupturing a segment about 550 km long of the Nazca–South America plate boundary fault parallel to the coastline. This earthquake triggered a destructive tsunami that affected the entire Pacific basin, especially the Chilean coast in an extension of ∼580 km. Here we analyze observations of currents and sea level anomalies caused by the tsunami that were recorded ∼30 km east of the epicenter by an RDI 600 kHz ADCP installed facing upward at 35 m depth. Although the ADCP sampling rate was not optimal for this kind of phenomenon, we were able to document for the first time near-field ocean hydrodynamics caused by an earthquake-triggered tsunami. We combine our observations with measurements of sea level recorded by tide gauges located along the Chilean coast. The ADCP recorded the passage of five waves of about 1.5–2 m amplitude during approximately 4 h after the earthquake. The first wave hit the coast in about 20 min with slow flows and propagated faster northwards (where the trench is deeper) than it did to the south. The first strong flow arrived cross-shore (after the first wave) with a vertical mean speed of 65 cm/s. Unlike this first cross-shore flow, the following peak flows were increasingly aligned with the coastline and had magnitudes that, in at least two cases, exceeded 70 cm/s. These flows were consistent with edge waves driven by the contact between the tsunami and the coastline. Current and sea level measurements had more energetic periods at 35, 50 and 72 min, displaying a coherent relationship with the dominant oscillation modes of large-scale resonance.

We investigated the ecological factors affecting net ecosystem metabolism (as the ratio of gross primary production to community respiration) by studying functional relationships between total and fractionated autotrophic biomass, heterotrophic prokaryote production, nutrients and net ecosystem metabolism, considering short-term (daily) and seasonal scales of variability in oceano- graphic conditions and wind stress. These studies were performed at 2 coastal upwelling sites off northern Chile (Chipana, ~21° S; Mejillones, ~23° S) in winter 2005, summer 2006, winter 2006 and summer 2007. Changes in the direction and persistence of the upwelling, which is driven by wind stress on a synoptic scale (6 d), appeared to be an important factor modulating phytoplankton size structure. Gross primary production did not show seasonality, probably because of the permanent equatorward wind regime off northern Chile. The phytoplankton community was dominated by the microphytoplankton size fraction (>20 µm), which was largely responsible for the variability of the total phytoplankton biomass. We found that the increase in contribution of large phytoplankton cells could generate net autotrophy in response to increased nitrate concentrations in the mixed layer, emphasizing that the degree of decoupling between gross primary production and community respi- ration may be primarily controlled by upwelling. Our results showed that the degree of coupling between heterotrophic prokaryote production and gross primary production as well as the amount of organic matter processed by prokaryotes vary with changes in the dominance of autotrophic and het- erotrophic processes in the microplanktonic community.

The southern Chilean region between the Boca del Guafo passage and Estero Elefantes contains one of the estuarine zones with the greatest freshwater influence on the planet. At the surface, plumes of freshwater from the fjord heads to their mouths, emptying into the Moraleda–Costa–Elefantes channel system and then the coastal ocean. The influence of this freshwater on the region’s estuarine dynamics, coastal ecology, and biogeochemical processes has only recently begun to be elucidated. Using hydrographic data from the CIMAR-Fiordos cruises (1998–2001), this study quantifies the equivalent height of freshwater, emphasizing the role it plays in the potential energy anomaly and front locations, as well as its relationship with river discharges. Using a criterion of equivalent height of freshwater >15% (density 3 and salinity 0.005 J/m 4 . The frontal zones were located in the extreme southeast of Jacaf Channel, at the head of Ventisquero Sound, in the central part of the Puyuguapi and Moraleda channels, and at the head and mouth of Aysen Fjord. The equivalent height of freshwater and potential energy anomaly showed a good correlation with the accumulated (5-day) river discharges ( r 2 =0.87), which were greatest toward the fjord heads in spring. The brackish surface water had short residence times (3.5 days) in Aysen Fjord, unlike the deep layer, which other authors report to have a longer residence time (near 1 year).

The COPAS research center (Universidad de Concepcion, Chile) initiated a time series station on the continental shelf off central Chile that is used for multi-disciplinary oceanographic research. In this manuscript, we analyze the temporal evolution (2002–2006) of hydrographic variables at this station related to annual cycles of surface winds, sea surface temperatures, net heat flux, and the local freshwater balance in terms of their coupling with coastal upwelling. Off central Chile, coastal upwelling is forced by seasonal variable winds along the coast, competing with two other seasonal processes that also modify the vertical density stratification of the water column. These processes are the mixed layer’s heat balance, which is dominated by solar radiation with maxima in January, and the fresh water balance, which is dominated by river discharge and precipitation with maxima in June and July. On a seasonal time scale, the temperature of the first 10 m of the water column closely follows the annual cycle of net surface heat flux, resulting in a shallow, warm mixed layer from December to April. The temperature below 15 m depth is controlled by seasonal coastal upwelling, which is favored by southerly alongshore winds in austral spring and summer and suppressed by mainly northerly winds in winter. Salinity is also determined on a seasonal scale, in the first 20 m of the water column, by the annual cycle of river discharge and precipitation and, below 25 m depth, by the seasonal upwelling pattern. Considering oxygen during spring and summer (the upwelling season), the 0.5 ml l−1 isoline rises – in extreme cases up to 20 m – thus, exposing the euphotic water column to hypoxic conditions.

Hydrographic and underway water velocity profiles were measured at the entrance to Concepcion Bay, an equatorward facing embayment in central Chile, in order to illustrate the wind-induced exchange flow. Observations took place over a 25-h period (5–6 January 2002) during the austral summer, which is characterized by upwelling winds in the region. One portion of the observational transect was directly influenced by the wind and the other was protected from such influence by an island. The portion of the transect influenced by wind showed a surface layer, delimited by a pycnocline, moving downwind owing to the direct action of wind stress. This surface transport should have caused an onshore decrease of surface elevation that would drive upwind flow below the surface layer. The portion of the transect protected by the island was influenced by its wake and perhaps forced by a semidiurnal tide. This study is one of the few observational examples of wind-induced flow that documents the wind-induced exchange pattern under weak internal friction (low Ekman number). This pattern consists of downwind flow in an upper layer delimited by the pycnocline and upwind flow below.

The distribution of pH and alkalinity has been used to calculate the distribution of total inorganic carbon (TC) and fugacity of carbon dioxide ( f CO 2 ) in the upper 200 m of the water column in coastal upwelling areas off northern Chile (23–24°S, near Antofagasta) and central Chile (30–31°S, near Coquimbo) during austral summer 1997. In these upwelling areas, colder surface waters were oxygen poor and strongly CO 2 supersaturated (100% near Antofagasta and 200% near Coquimbo), although below the pycnocline the CO 2 supersaturation invariably exceeded 200% in both areas. The larger surface CO 2 supersaturation and outgassing at 30°S were associated with stronger winds that promoted the upwelling of denser water (richer in CO 2 ) as well as a higher air–sea CO 2 transfer velocity. The consistent decrease in intensity of the southerly winds (as derived from NSCAT scatterometer data) from 30–31°S to 23–24°S suggests a corresponding decline in the intensity of the CO 2 outgassing due to upwelling. Additionally, we suggest here that the intensity of the local upwelling forcing (i.e. alongshore–equatorward winds) plays a role in determining the water mass composition and phytoplankton biomass of the coastal waters. Thus, while deep upwelling of salty and cold water resulted in high f CO 2 (up to 1000 μatm) and very low phytoplankton biomass (chlorophyll a concentration lower than 0.5 mg m −3 ), the shallow upwelling of less salty (e.g. salinity 2 -supersaturated water resulted in a higher phytoplankton biomass, which further reduced surface water f CO 2 by photosynthesis.

We combined on-deck and in situ measurements and satellite-derived data to study the spatial variability of springtime size-fractionated primary production and chlorophyll-a biomass along gradients of hydrographic conditions and surface PAR in central and northern Chilean Patagonia (41–50°S). This extensive and fragmented region encompasses numerous fjords and channels, as well as the northern and southern icefields (46–47°S, 48–52°S). Primary production displayed a latitudinal pattern decreasing southwards (6-fold lower), particularly toward areas influenced by rivers with a nival regime. Micro-phytoplankton (>20 μm) dominated the primary production (57–93%) and chlorophyll-a (43–91%) of northern sites, where warmer and more saline surface waters exhibit greater PAR irradiance. Small phytoplankton cells ( 50% of carbon fixation and chlorophyll-a in the southernmost sites, especially those located near glaciers and major rivers, where surface temperature, salinity, and PAR irradiance were lowest. The long-term (2002–2012) average field of springtime PAR derived from satellite imagery showed a southward increase in longitudinal gradients, which indicates that spatial changes in surface light attenuation along this region are largely driven by glacier-derived freshwater inputs. A principal component analysis of surface temperature, salinity, and PAR produced an ordination of sites that was consistent with spatial changes in the balance of oceanic versus riverine influence on surface conditions along this region. Total primary production was significantly correlated (r = 0.61, p = 0.007) with the first principal component, which explained 65% of joint variability in hydrographic conditions and PAR. The same principal component clearly separated sites in northern Patagonia where micro-phytoplankton dominated total primary production – along the Reloncavi fjord and Inner Sea of Chiloe – from those located further south where other size fractions were equally or more important. We stress the need to include spatial variability in nutrient concentrations, which together with the strong light attenuation induced by glacier-derived freshwater may further explain the spatial patterns in primary productivity, phytoplankton biomass, and carbon fluxes along Chilean Patagonia.

Coldfilaments associatedwith Eastern Boundary Currents are typically narrower than 100 km but can be several hundred kilometers long, extending from the coast to the open ocean in upwelling areas. One such structure, observedoff Pen ! de Mejillones (231S, Chile), was studied with both satellite images and two 5-days hydrographic cruises carried out during January 1997. The study used a coastal grid of 31 stations in an area of 165 � 155 km 2 , approximately. The spatial distribution of the filament and its change between cruises are described from the horizontal distributions of dynamic height, temperature, salinity and dissolved oxygen. The filament was a shallow feature (thickness o100 m) andextend edat least 165 km toward the open ocean. A meandering northward current flowed at the borders of the filament, separating oceanic andcoastal waters of d ifferent physical properties. Comparisons of cross sections of the filament near the coast andin the oceanic zone show the ascent of the shallow salinity minimum (SSM), andits extension towardthe ocean, boundto the filament. It is conclud edthat Subantarctic Water ((SAAW) distinguish by low salinity, high dissolved oxygen) and Equatorial Subsurface Water ((ESSW) high salinity, low dissolved oxygen, high nutrient content) form this filament, and that their relative proportions depend on the strength of the coastal upwelling. Thus, the knowledge of the dynamics of these structures is fundamental to better understanding of the spatial distribution of important biological variables, such as nutrients andchlorophyll, in the coastal ecosystem. r 2001 Elsevier Science Ltd. All rights reserved.

The submarine canyon of the Biobio River (36850 0 S; 73815 0 W) is located in the vicinity of a zone of intense seasonal upwelling o Central Chile. This zone conforms a coastal ecosystem that produces more than 50% of the Chilean fish catch and approximately 4% of the world fish captures. As the small- and mesoscale oceanographic processes associated to this canyon are practically unknown, it has not been demonstrated whether the interaction of the canyon with the coastal ecosystem contributes to the high biological productivity. Using horizontal currents and hydrographic variables measured in and around this canyon, this study shows the first evidences of the rise of water through the canyon of the Biobio River. Water velocities were measured using three moorings, deployed near the head and the flanks of the canyon in two periods of the year (March-April and August 1991). During the first period, when the wind conditions were relatively constant, both sides of the canyon had dierent circulation patterns. The kinetic energy of bottom currents in the northern side, which is associated to the continental shelf, was at least one order of magnitude larger than in the southern side, which is associated to interior waters. During the second period a storm of northerly winds, non-favorable for upwelling, generated a mixing of the water column down to 50m, approximately. Two days after the beginning of the storm the water column under 60m depth cooled down. This cooling responded mainly to the northerly and coastward currents that were generated almost at the end of the storm. Cooling was more evident at the northern side of the canyon, with cooling rates of 0.58C/day. Ascent rates of 0.02cm/s for the 118C isotherm and 0.03cm/s for the 10.58C isotherm were estimated. The divergence of the currents, calculated at 40m depth, also indicates the rise of cold waters through the canyon during and after the storm. # 2001 Elsevier Science Ltd. All rights reserved.

Sedimentation rates of faecal material, phytoplankton and microzooplankton and production rates of faecal material from crustaceans and pelagic tunicates were estimated during the austral summer and winter 1997, and summer 1998. in the northern Humboldt Current (23°S, off Antofagasta, Chile). Sampling periods covered pre-El Nino (January 1997) and El Nino 1997-98 (July 1997 and January 1998). Samples were collected using floating sediment traps deployed at 65, 100, 200 and 300 m depth in oceanic and coastal areas. Sedimentation rates during January 1997 were, on average, 152 ± 23 and 85 ± 57 mg C m 2 day -1 at 65 and 300 m depth, respectively. During July, these rates averaged 93 ± 56 mg C m 2 day -1 at 65 m depth and 35 ± 12 mg C m 2 day -1 at 300 m depth, while in January 1998 they were 98 and 109 ± 37 mg C m 2 day -1 at 65 and 200 m depth, respectively. Recognizable faecal material made up the hulk of the sedimenting matter, accounting for 8 ± 5% (n = 14), 31 ± 26% (n = 16) and 8 ± 5% (n = 5) of the average total organic carbon recorded from all sediment trap samples collected during January and July 1997 and January 1998, respectively. However, at 300 m depth, the contribution of recognizable faecal material to total sedimented organic carbon increased to 43 ± 33% (n = 4) during July 1997. The remaining sedimenting particles consisted mainly of tintinnids, crustacean exuviae, heterotrophic dinoflagellates (both thecated and athecated) and diatom cells. During this study, we estimated that only a minor fraction (average ± SD = 5 ± 8%) of the copepod faecal material produced within the photic zone sedimented down to 300 m depth, suggesting an efficient recycling within the overlaying water column. On the other hand, an important fraction (47 ± 30%) of the euphausiid faecal strings was collected in the 300 m depth trap, suggesting that this material would enhance the downward flux of particulate organic matter (POC). POC fluxes to 65 and 300 m depth traps were in the range of 4-20% and 3-8% of the estimated primary production during the whole study period. It is postulated that the overall vertical flux of particulates and, in particular, faecal pellets was determined by a combination of three factors. The first was the composition of the zooplankton assemblages in the study area. When the dominant group was calanoid copepods, their faeces seemed to contribute poorly to the vertical flux of particulates. On the other hand, when the dominant group was euphausiids, a significant proportion of their faecal material was collected in the sediment trap located at 300 m depth. The second was the relatively high abundance of cyclopoid copepods from the genera Oncaea, Corycaeus and Oithona, which are reported to feed on aggregates of phytodetritus and faecal pellets produced by calanoid copepods, suggesting that they may act as a natural filter to sedimenting particulates. The third was the composition and size e spectrum of the phyto- and microzooplankton assemblages which are potential food sources for the meso- and macrozooplankton. These factors were partially modulated by both the 1997-1998 El Nino and seasonality.

A multi-disciplinary research program was conducted in the northern Humboldt Current System in a 80 X 80 nautical n7ile area off Antofagasta, northern Chile (23" S) on 3 occasions: before the 1997/98 El Nirio event (January 1997), and dunng the onset and maximum penods of the event (July 1997 and January 1998, respectively). As a part of this program, the trophodynamic role of pe lag~c tunlcates (salps and appendiculanans), as well as the crustacean zooplankton, divided into 3 size classes (large[euphauslids], medium[large calanoid copepods] and small-size animals [small calanoid and cyclopoid copepods]) were assessed One of the most conspicuous physical processes was the deepenlng of the thermocline during the El Nirio event, which in turn led to suppression of nutrient enrichment by upwelling events and low chlorophyll a (chl a ) concentrations in the study area. Chl a and particulate organlc carbon (POC) values were hlgher near the coast, and coastaWoceanic gradients were greater m the case of chl a. High chl a (100 to 160 mg m-') and POC ( l 1 to 17 g m-2) concentrations were usually found associated with bays and/or capes w~thin 40 nautical miles of the coast. In contrast, oceanic areas showed low concentrations throughout the study. Small calanoid and cyclopoid copepods represented only a minor fraction of the total crustacean zooplankton carbon (4 to 20%), although they often accounted for a relatively large portion of the total ingestion (26 to 68%) of the crustacean zooplankton community. Euphausiids represented a large fraction of total crustacean zooplankton carbon (28 to 73 %), and accounted for between 5 and 61 % of total crustacean zooplankton grazing. Ingestion rate as a percentage of body carbon was negatively correlated with animal size, varying between 4 % in euphausiids (17 mm) and 123% in small calanoid copepods (0.8 to 1.7 mm). A companson of estimated daily respiration rates and daily carbon ingestion rates indicated that ingestion of phytoplankton would have exceeded respiratory demands for both large and small calanoid copepods during all 3 sampling periods. In contrast, ingestion of phytoplankton failed to account for the respiratory needs of the euphausiids. This, together with microscopical observations, led to the conclusion that euphausiids utilised other sources of carbon such as detritus, microand mesozooplankton in addition to phytoplankton. Crustacean zooplankton showed a s~gnificant grazing impact, removing from 10 to 34 % of primary production (PP). Salps of the species Salpa fuslformis were present in dense aggregates that could have removed up to 60% of PP during January 1997. On average, the grazing impact of this specles was approximately one-half (16%) that of the whole crustacean zooplankton community combined (34 %). We did not find any significant difference in zooplankton biomass between January 1997 (nonEl Nino) and January 1998 (El Nino), with average biomasses of 24.6 and 21.4 mg dry wt m-" respectively. There was, however, a shift in the size spectrum of crustacean zooplankton towards small-sized copepods between January 1997 (60 mg C m-') and January 1998 (186 mg C m-2)

We have studied the seasonal variability of four turbid river plumes along the central Chilean coast using daily, high-resolution images of surface turbidity from MODIS (Moderate Resolution Imaging Spectroradiometer) in combination with measurements of wind, river flow, and hydrographic data. Atmospherically corrected MODIS data reveal strong seasonal variability in the areal extent of plume water, as well as in turbidity levels, which are significantly correlated with seasonality in river discharge. A seasonal climatology of turbid plume patterns shows individual plumes merging into an extensive body of turbid waters attached to the coast during fall (April–June)–winter (July–September) (occurs about 10% of days in fall–winter). During spring (October–December) and summer (January–March), the individual plumes remain distinct and occupy a smaller area close to the coast, when observed (evident on less than 30% of days in spring–summer). In spring–summer most plumes are detected for the northern rivers (Mataquito and Maule). When the plumes merge into a coastal band in fall–winter, a turbid area of more than 1000 km2 is observed in the study area between 34.85°S and 37.15°S. This occurs following peaks in river discharge combined with the effect of strong southward (downwelling-favorable) winds. An analysis of key non-dimensional numbers shows that buoyancy dominates plume dynamics during summer, whereas inertial forcing associated with river outflow is more important in winter near the coast. Farther offshore (> 10 km), the effects of rotation and wind tend to dominate the plume dynamics.

[1] Sea surface wind data from the QuikSCAT satellite and two meteorological stations collected over 1 decade (1999–2008) were used to study the dominant time scales of the wind regime in the Yucatan basin. Wind data were used to quantify its implications on regional hydrodynamics by evaluating Ekman pumping and Ekman transport. The annual cycle of surface wind revealed different features than the Caribbean wind regime with a relative wind stress maximum observed in the Yucatan basin in June caused by the Caribbean low-level jet. The strongest wind stress occurred during November presumably due to the collapse of the Atlantic warm pool. This feature provides new evidence of the importance of local atmosphere-ocean coupling. Synoptic scale variability was detected during fall and winter, leaving spring and summer almost free from these activities. Empirical orthogonal functions revealed three dominant time scales of variability: an annual scale in mode 1 (46.3% of the total variance), a synoptic scale in mode 2 (27.7%), and a semiannual scale in mode 3 (6.4%). The third mode featured extreme pulses (six tropical storms and nine hurricanes). Ekman transport was found to contribute the most (93%) to total transport, whereas Ekman pumping contributed only 7%. However, upwelling induced by Ekman pumping persisted during some synoptic pulses, underscoring the importance of tropical storms and hurricanes. Offshore Ekman transport over the continental shelf north of the Yucatan Peninsula favored upwelling all year long. Onshore transport toward the coasts of southern Cuba and the eastern Yucatan Peninsula favored downwelling.

We characterize the response of diurnal-period ocean current variability to the sea breeze using measurements of current velocity taken off the mouth of the Itata River and wind stress collected at Hualpen Point (central Chile) in spring of 2007 and summer of 2006 and 2008. During these three periods, the winds are predominately towards the northeast, following the coastal topography, with the highest variability found in the near-diurnal and synoptic frequency bands. The sea breeze amplitude is intermittent in time and is associated with synoptic-scale variability on the order of three to 15 days, so that the diurnal-period winds (and currents) are enhanced when the alongshore wind (i.e. upwelling-favorable) is strong. The water current variability in the near-diurnal band is significant, explaining up to 40% (spring 2007) of the total current variance in the first 15 m depth. The response of the near-diurnal band to the sea breeze is surface-intensified and elliptically polarized with anticlockwise rotation. As is the case with the wind, the ellipses of the daily-period surface current velocity are oriented alongshore, although the currents are significantly less rectilinear. In the along-shore direction, the diurnal-period wind-stress is directed towards the northeast and the shore after mid-day and reverse their direction at night. The currents also show counterclockwise rotation during the day, with nearly in-phase along-shore motion in the surface layer and shoreward (oceanward) motion during the morning (late afternoon). The deep layer also show significant counterclockwise motion but its magnitude is roughly one third smaller than in the surface layer, and as much as 180° out of phase. A two-layer analytical model with no friction but that includes a cross-shelf pressure gradient and wind-stress forcing is used to diagnose key properties of the observed response, suggesting that the observed diurnal-period currents may be wind driven. However, data from different years shows that inertial motions and probably other dynamics can be important when the winds are relatively weak or highly variable.

[1] The subinertial flow on the continental shelf off Concepcion (central Chile) and its relation with the local wind-forcing and the topography are studied. Emphasis is placed on the three-dimensional aspects and the effect of the topography on the classical two-dimensional approach to the coastal upwelling. Time series coming from 18 current meters installed on six moorings during March–April 1994 were analyzed. Hydrographic data were collected during two hydrographic cruises (6–7 March and 30–31 March). Complementary information includes wind data and sea level. Empirical orthogonal functions using all series showed two principal subinertial flow patterns. The first mode corresponds to an alongshore flow responding to the intensification of southwesterly wind on a 3- to 10-day scale. The second mode is dominated by the cross-shore fluctuations at the shelf break. The importance of the local wind-forcing appears clearly when comparing the theoretical and observed Ekman transport in the north and central shelf (R = 0.8). Near the bottom a mean southward flow was found with a clear southward intensification induced by the bathymetry and probably by a meridional pressure gradient. This bottom flow modifies the typical coastal upwelling pattern through an offshore Ekman transport in the surface and bottom layers. This implies that the compensation flow for the coastal divergence comes from intermediate waters that arrive onto the shelf through ageostrophic process related with the submarine canyons located toward the north and south of the shelf.

Changes in oceanographic conditions and zooplankton community structure were investigated during a five year period, which included the 1997-98 El Niño (EN), in the coastal region off Antofagasta (23ºS), northern Chile. We aimed at examining the changes in abundance and size composition of zooplankton, as well as the main oceanographic changes associated with the onset and evolution of the EN, This study was supported by FONDECYT Grant 1000419, 5960002-1996 and PCCI CONICYT/CSIC 2000-2-083

Large numbers of gelatinous zooplankton were collected off Mejillones Peninsula, Chile (Humboldt Current System) in January 1997 during an oceanographic cruise. The area was characterized by the mixing of 3 water masses and the development of coastal upwelling. Siphonophores were the predominant group at most of the stations and the calycophoran Bassia bassensis was overwhelmingly the most abundant species. Five group associations were distinguishable in relation to the water masses identified. Siphonophores were associated with Subtropical Surface Water, the ctenophore Pleurobrachia sp. with Subantarctic Water, the pelagic tunicate Salpa fusiformis with Equatorial Subsurface Water, an assemblage of all gelatinous groups with mixed waters, and a low occurrence of gelatinous groups with upwelled Equatorial Subsurface Water. Molluscs were the group least associated with any water mass. The potential percentage of small copepods removed by B. bassensis ranged between 2.9 and 69.3%. Our results indicate that B. bassensis was the most important secondary predator in the top 50 m of the water column, and could therefore have had a significant trophic impact on the population of small copepods off the Mejillones Peninsula during the sampling period, where small copepods constituted 80.6 % of the total mesozooplankton community. This siphonophore potentially ingested an average of 17.3 % of the total copepod biomass