The relationship between chromophoric dissolved organic matter and dissolved organic carbon in the European Atlantic coastal area and in the West Mediterranean Sea (Gulf of Lions)

The absorption coefficient of chromophoric dissolved organic matter (aCDOM) has been found to be correlated with fluorescence emission (excitation at 355 nm). In the coastal European Atlantic area and in the Western Mediterranean Sea (Gulf of Lions), a significant statistical dependence has been found between aCDOM and fluorescence with dissolved organic carbon (DOC) concentration. The relationship shows that, in the river plume areas (Rhine in the North Sea and Rhône in the Gulf of Lions), a consistent fraction of DOC (from 40% to 60% of the average of the DOC measured) is non-absorbing in visible light range, where the dissolved organic matter (DOM) is typically absorbent. In comparison, in the open sea, apparently not affected by the continental inputs, the entire DOC belongs to the chromophoric DOM whose specific absorption is lower (5 to 10 times) than that found in the river plume areas.     

Benthic remineralization at the land–ocean interface: A case study of the Rhône River (NW Mediterranean Sea)

Biogeochemical processes in sediments under the influence of the Rhône River plume were studied using both in situ microelectrodes and ex situ sediment core incubations. Organic carbon (OC) and total nitrogen (TN) content as well as stable carbon isotopic composition of OC (δ¹³C_OC) were analysed in 19 surface sediments to determine the distribution and sources of organic matter in the Rhône delta system. Large spatial variations were observed in both the total O₂ uptake (5.2 to 29.3 mmol m⁻² d⁻¹) and NH₄⁺ release (−0.1 to −3.5 mmol m⁻² d⁻¹) rates at the sediment–water interface. The highest fluxes were measured near the Rhône River mouth where sedimentary OC and TN contents reached 1.81% and 0.23% respectively. Values of δ¹³C_OC ranged from −26.83‰ to −23.88‰ with a significant seawards enrichment tracing the dispersal of terrestrial organic matter on the continental shelf. The amount of terrestrial-derived OC reaches 85% in sediments close to the Rhône mouth decreasing down to 25% in continental shelf sediments. On the prodelta, high terrestrial OC accumulation rates support high oxygen uptake rates and thus indicating that a significant fraction of terrestrial OC is remineralized. A particulate organic carbon (POC) mass balance indicates that only 3% of the deposited POC is remineralized in prodelta sediments while 96% is recycled on the continental shelf. It was calculated that a large proportion of the Rhône POC input is either buried (52%) or remineralized (8%), mostly on the prodelta area. The remaining fraction (40%) is either mineralized in the water or exported outside the Rhône delta system in dissolved or particulate forms.     

Dissolved Cd behaviour in some selected french and chinese estuaries. Consequences on Cd supply to the ocean

Few data on dissolved trace metals in rivers and estuaries are presently available. This paper is an attempt to provide additional data on dissolved concentrations obtained in polluted and so-called unpolluted river estuarine systems. Data for two major French rivers (Gironde, Rhône) have been compared with the Chinese Yellow River (Huanghe) and Yangtze River (Changjiang). Dissolved Cd concentrations have been measured by differential pulse anodic stripping voltammetry. Average concentrations range from 15 ng kg⁻¹ to 50 ng kg⁻¹ (0.13–0.45 nmol kg⁻¹) in the French rivers and are below 4 ng kg⁻¹ (0.040 nmol kg⁻¹) in the Chinese rivers.In all the estuaries studied the dissolved Cd concentrations depict a systematic bulge in the mixing zone which is attributed largely to remobilization processes from particulate matter when the chlorinity increases. Other parameters that may also play a significant role for remobilization are discussed. The processes concerned lead us to reassess the net Cd river input to the oceans, and this should be taken into account for a more precise evaluation of the residence time of oceanic Cd.     

Dissolved and particulate aluminum in the Columbia River and coastal waters of Oregon and Washington: Behavior in near-field and far-field plumes

The distribution of dissolved (soluble and total) and particulate (leachable and total) aluminum was examined in the Columbia River and estuary, in near-field and far-field river plumes, and in adjacent coastal waters of Washington and Oregon during the River Influence on Shelf Ecosystems (RISE) cruise of May/June 2006. Dissolved and particulate aluminum (Al) concentrations were significantly greater in the river than in the coastal waters that mixed to form the plume. Dissolved Al concentrations in the Columbia River (∼80 nM) were low relative to other major rivers. Leachable and total particulate Al concentrations within the river reached concentrations greater than 1000 nM and 18,000 nM, respectively. Dissolved Al within the Columbia River estuary showed a significant removal (∼60%) at salinities between 0 and 10 with salt-induced flocculation of colloidal Al complexes and enhanced particle scavenging being probable explanations for aluminum removal. Dissolved and particulate Al concentrations were significantly greater in near-field plumes relative to surrounding coastal waters. As the plume advected from near-field to far-field away from the river mouth, dilution of the plume with lower dissolved Al surface waters as well as particle scavenging along the flow path appeared to be controlling dissolved Al distributions. Particle settling as well as dilution with lower particle-load waters led to observed decreases in particulate Al as the plume moved from near-field to far-field. However, the percent-leachable particulate aluminum in both near-field and far-field plumes was remarkably constant at ∼7%. Dissolved and particulate Al in a far-field plume over 100 km southwest of the Columbia River mouth were over an order-of-magnitude greater than surrounding waters, illustrating the importance of the Columbia River plume as a mechanism for transporting Al offshore. Aluminum could be used to trace the input of biologically-required elements such as iron into waters off the shelf.     

Deep strong currents and sediment transport in the Northwestern Mediterranean Sea

The Petit Rhône Canyon (Gulf of Lions) is incised by a narrow meandering thalweg. Two current meters were moored near the bottom, one in the channel and the other on the levee. None of the measured currents is associated with the sediment transport peculiar to deep-sea fan building. This transport is mainly influenced by relatively high speeds (1 h means up to 48 cm/s; 1 day means > 30 cm/s) measured in diverse directions.     

Evaluation of anthropogenic and biogenic inputs into the western Mediterranean using molecular markers

Aliphatic hydrocarbons (AHs), sterols (ST), and lipid classes were determined in suspended particles collected in the Catalan Sea, northwestern Mediterranean. Principal Component Analysis of the data set revealed a clustering of samples depending on the sources of organic matter, i.e., coastal influenced, open sea and frontal zone. Terrestrial inputs were recognized in particles collected in the surface waters, at the vicinities of river outflow (i.e., Rhône and Ebro), by a predominance of C₂₉ and C₃₁ n-alkanes, 24-ethylcholest-5-en-3β-ol (S12), and the anthropogenic 5β(H)-cholestan-3β-ol, coprostanol (S1). Phytoplanktonic molecular markers (n-C₁₇, 27-nor-24-methylcholesta-5,22E-dien-3β-ol, cholesta-5,22-dien-3β-ol and 24-methylcholest-5-en-3β-ol) were widespread but relatively more apparent in the open sea and frontal zones. A similar distribution was observed for lipid classes, with higher concentrations of phospholipids, and an enrichment in free fatty acids in the areas influenced by river discharges. Total sterol, the unresolved complex mixture of hydrocarbons and the pristane–phytane ratio were highest at a persistent frontal zone, possibly reflecting the combination of a higher primary productivity and fossil hydrocarbon absorption on to suspended particles. Moreover, vertical profiles exhibited a subsurface concentration maximum at 20–30 m water depth, concurrently with the chlorophyll.     

Understanding shallow gas occurrences in the Gulf of Lions

New coring data have been acquired along the western Gulf of Lions showing anomalous concentrations of methane (up to 95,700 ppm) off the Rhône prodelta and the head of the southern canyons Lacaze-Duthiers and Cap de Creus. Sediment cores were acquired with box and kasten cores during 2004–2005 on several EuroSTRATAFORM cruises. Anomalous methane concentrations are discussed and integrated with organic carbon data. Sampled sites include locations where previous surveys identified acoustic anomalies in high-resolution seismic profiles, which may be related to the presence of gas. Interpretation of the collected data has enabled us to discuss the nature of shallow gas along the Gulf of Lions, and its association with recent sedimentary dynamics. The Rhône prodelta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried, effectively removing this organic matter from aerobic oxidation and biological uptake, and leading to the potential for methanogenesis with burial. Away from the flood-related sediments off the Rhône delta, the organic matter is being reworked and remineralized on its way along the western coast of the Gulf of Lions, with the result that the recent deposits in the canyon contain little reactive carbon. In the southernmost canyons, Lacaze-Duthiers and Cap de Creus, the gas analyses show relatively little shallow gas in the core samples. Samples with anomalous gas (up to 5,000 ppm methane) are limited to local areas where the samples also show higher amounts of organic matter. The anomalous samples at the head of the southern canyons may be related to methanogenesis of recent drape or of older sidewall canyon infills.     

C18 Sep-Pak Extractable Dissolved Organic Copper Related to Hydrochemistry in the North-west Mediterranean

Extractable organic copper using C18 Sep-Pak cartridges was investigated in seawater after laboratory experiment showed that the (C18 Sep-Pak) cartridges were reliable, in open and coastal waters with normal levels of dissolved organic carbon, for the separation of a specific fraction of organo-copper complexes.Given that the Sep-Pak cartridges retain the hydrophobic fraction of the dissolved organic matter, this extraction technique was applied for studying the characteristics of this particular hydrophobic dissolved organic copper fraction (hDOCu) in the north-western Mediterranean waters. Surface distribution of hDOC is influenced by organic matter input from the river Rhone and its estuary as well as the physical processes affecting the primary productivity such as coastal upwelling. By correlating hDOCu concentrations with total dissolved copper and other hydrochemical data such as salinity and dissolved organic carbon, it was possible to examine the behaviour of hDOCu in the water masses of different sources and ages.Marine organic matter has been shown to have high complexing capacity. Productive superficial and intermediate waters as well as deep waters showed relatively high and comparable complexing capacity indicating that old organic matter may have strong complexing sites.     

Anthropogenic vs. lithogenic origins of trace elements (As, Cd, Pb, Rb, Sb, Sc, Sn, Zn) in water column particles: northwestern Mediterranean Sea

The distribution of heavy metal was analyzed in water column particles collected in autumn (October 1985) and spring (March 1986) by two series of sediment traps from a mooring located in the northeastern Mediterranean Sea continental slope. Four traps were set, at 50, 100, 300, 600 m depths on the mooring in 645 m deep water in the Lacaze-Duthier canyon. The total metal concentrations were determined by ICP-MS. Results show that Rb and Sc contents display typical shale values. As, Cd, Pb, Sb, Zn (normalized to Sc) display high enrichment factors (up to 50) over shale compositions. Distinctive temporal variability as well as the respective contributions of local (Têt, Aude) and remote (Rhône) rivers and Sahara-derived aerosols have been identified. Fluxes of most elements observed in the upper 100 m can be attributed to atmospheric fluxes. In the deepest traps (300 and 600 m) these fluxes are, however, mostly dominated by riverine particles advected from the continental shelf. Most of the trace-element enrichments are more likely to be related to the anthropogenic input rather than to biological cycling. Isotopic composition of lead determined by ICP-MS enabled to evaluate that the proportion of anthropogenic lead derived from European gasoline consumption ranged between 50 and 100%.     

Nitrate reductase activity and the speciation of selenium at the mouth of Chesapeake bay

Nitrate reductase activity and the concentrations of selenite and selenate were monitored for six months at the mouth of Chesapeake Bay (USA). A positive correlation was found between nitrate reductase activity and the concentration of selenite, suggesting that selenite may be formed in coastal waters and nitrate reductase may be involved in the process.     

Live (stained) benthic foraminifera from the Rhône prodelta (Gulf of Lion,NW Mediterranean): Environmental controls on a river-dominated shelf

In this paper, we investigate the ecology of live (rose Bengal stained) benthic foraminifera collected at 20 stations ranging from 15 to 100 m depth in the Rhône prodelta (Gulf of Lions, NW Mediterranean). These sites were sampled in September 2006, five months after the Rhône River annual flood. Statistical analyses based on foraminiferal communities (> 150 μm) divide our study area into six main biofacies directly related to environmental conditions. Miliolid species are abundant in the relict prodeltaic lobe which is characterised by sand with low organic matter content. Close to the river mouth, the limited oxygen penetration in the sediment combined with important hydro-sedimentary processes constitute stressful conditions for foraminiferal faunas dominated by opportunistic species (e.g. Leptohalysis scottii). With increasing distance from the river mouth, foraminiferal faunas (e.g. Nonionella turgida, Eggerella scabra) adapted to thrive in sediments enriched in Rhône-derived organic matter under more stable hydro-sedimentary conditions appear. In the distal part of the Rhône River influence, benthic species (e.g. Valvulineria bradyana, Textularia agglutinans) living in fine sediment enriched in both continental and marine organic compounds emerge. At the deepest stations located in the south-eastern part of our study area, benthic foraminiferal faunas (e.g. Bulimina aculeata, Melonis barleeanus, Bigenerina nodosaria) are highly diverse, underlining stable environmental conditions characterised by marine-derived organic matter supplies and relatively deep oxygen penetration depth in the sediment. We also compare foraminiferal faunas sampled in September 2006 with communities sampled in June 2005, one month after the Rhône River annual flood (Mojtahid et al., 2009). This comparison suggests that opportunistic species (e.g. B. aculeata, Cassidulina carinata, V. bradyana) have responded to organic matter inputs related to marine primary production in June 2005.     

Dissolved iodine across the Gulf Stream Front and in the South Atlantic Bight

The distributions of iodide, iodate and total iodine were determined along a transect from the Sargasso Sea and across the Gulf Stream to the continental shelf of the South Atlantic Bight during November 1990. The western boundary of the Gulf Stream at the outer shelf-upper slope was characterized by steeply sloping isotherms and isopleths of iodide and iodate, resulting from a dome of cold water that was rich in iodate and nearly devoid of iodide at the slope. Both the mid and the inner shelf were relatively well mixed vertically. The concentration of iodate in the surface waters decreased shoreward from >0.3 μM in the Sargasso Sea/Gulf Stream/outer shelf, to 0.29 μM in the midshelf, 0.19 μM in the outer-inner shelf and 0.11 /IM in the inner-inner shelf. Concomitantly, the concentration of iodide increased from <161 nM to 175 nM, 257 nM and 300 nM. The concentration changes were more abrupt in the inner-inner shelf within about 30 km from the shore. There was no evidence of significant concentrations of organic iodine. These distributions of iodide and iodate suggest that the South Atlantic Bight may act as a geochemical processor of dissolved iodine. Iodate is added to the shelf during topographically induced upwelling and frontal exchange with the Gulf Stream. In the shelf waters, iodate is reduced to iodide in situ. Iodide is exported from the shelf to the Gulf Stream which may eventually further transport it to the ocean interior. A ☐ model calculation suggests that 28% and 43% of the iodate added to the Bight and the inner shelf, respectively, are converted to another form in these waters, almost all of which is iodide. About a third of the reduction of iodate to iodide in the Bight occurs in the inner shelf. Thus, the inner shelf may be the most geochemically active zone within the Bight. The residence times of iodide relative to its production and that of iodate relative to its removal are 3.1 and 3.6 months in the Bight and 0.9 and 1.8 months in the inner shelf.     

Influence of atmospheric inputs on the iron distribution in the subtropical North-East Atlantic Ocean

Aerosol (soluble and total) iron and water-column dissolved (DFe, < 0.2 μm) and total dissolvable (TDFe, unfiltered) iron concentrations were determined in the Canary Basin and along a transect towards the Strait of Gibraltar, in order to sample across the Saharan dust plume. Cumulative dust deposition fluxes estimated from direct aerosol sampling during our one-month cruise are representative of the estimated deposition fluxes based on near surface water dissolved aluminium concentrations measured on board. Iron inventories in near surface waters combined with flux estimates confirmed the relatively short residence time of DFe in waters influenced by the Saharan dust plume (6–14 months). Enhanced near surface water concentrations of DFe (5.90–6.99 nM) were observed at the Strait of Gibraltar mainly due to inputs from metal-rich rivers. In the Canary Basin and the transect towards Gibraltar, DFe concentrations (0.07–0.76 nM) were typical of concentrations observed in the surface North Atlantic Waters, with the highest concentrations associated with higher atmospheric inputs in the Canary Basin. Depth profiles showed that DFe and TDFe were influenced by atmospheric inputs in this area with an accumulation of aeolian Fe in the surface waters. The sub-surface minimum of both DFe and TDFe suggests that a simple partitioning between dissolved and particulate Fe is not obvious there and that export may occur for both phases. At depths of around 1000–1300 m, both regeneration and Meddies may explain the observed maximum. Our data suggest that, in deep waters, higher particle concentrations likely due to dust storms may increase the scavenging flux and thus decrease DFe concentrations in deep waters.     

Processes influencing iron distribution in the coastal waters of the Tsugaru Strait,Japan

We report measurements of iron, nutrients, dissolved oxygen, humic-type fluorescence intensity and chlorophyll a concentrations in the coastal waters at the inflow (western) and outflow (eastern) ends of Tsugaru Strait (Japan) in June 2003 and 2004. Two different water masses (intensive eastward flow “subtropical Tsugaru Warm Current Water (TWCw)” and weak westward flow “subarctic Oyashio Water (OW)”) were observed at the eastern end of the strait. TWCw at the southern part of the eastern strait was vertically homogeneous with a uniform concentrations of iron (0.7–1.1 nM for labile dissolved Fe and 14–20 nM for total dissolvable Fe in 2003) as well as other chemical, biological and physical components throughout the water column of 200 m due to strong vertical mixing in the strait. The degree of mixing in the Tsugaru Warm Current (TWC) is predominantly affected by diurnal tidal current, which is strong during the period of tropical tides and weak during the period of equinoctial ones. The especially strong vertical water mixing in 2003 is caused by large dissipation energy input due to the bottom friction of passage-flow through the strait and tidal current. At the northern part of the eastern strait, the fresh surface layer overlying the OW and the deep-bottom waters in 2003 contained large concentrations of dissolved iron, resulting from iron supplied from river runoff and shelf sediments, respectively. These results suggest that the most important mechanism for transporting iron in the strait is the strong vertical water mixing due to the tidal current, and that the iron sources in the coastal waters are the organic-associated, iron-rich freshwater input into the surface water.     

Nitrogen and phosphorus species in the coastal and shelf waters of Southeastern North Carolina, Mid-Atlantic U.S. coast

The diversity of small-scale wetlands, high salinity tidal creeks, salt marshes, estuaries, and a wide and shallow shelf with the Gulf Stream close to the break makes the coastal zone of south-eastern North Carolina (U.S.) a natural laboratory for the study of the cycling of nitrogen (N) and phosphorus (P) in coastal and shelf waters. We assessed the summer concentrations, forms, and ratios for each N (total dissolved N, nitrate + nitrite, ammonium and dissolved organic N) and P (total dissolved P, o-phosphate and dissolved organic P) pool as these nutrients travel from tidal creeks, salt marshes and two large estuaries to Long and Onslow Bays. Additionally, we measured ancillary physical (temperature, salinity and turbidity) and chemical (dissolved oxygen, chlorophyll a and pH) water properties. Highest concentrations of all individual N and P compounds were found in the upper parts of each tributary and were attributed to loads from agricultural and urban sources to the coastal watersheds, continuing downstream to receiving estuaries. In all areas, dissolved organic N and P species were predominant constituents of the total dissolved N and P pools (64–97% and 56–93%, respectively). The lower parts of estuaries and surface shelf waters were characterized by oceanic surface values, indicating removal of N and P downstream in all tributaries. The different watershed and hydrological characteristics also determined the different speciation of N and P pools in each estuary. Despite a high level of anthropogenic pressure on the uppermost coastal waters, there is self-regulation in this coastal ecosystem with respect to human perturbations; i.e. significant amounts of the N and P load are retained within estuarine and nearshore waters without reaching the shelf.     

Molecular weight and chemical reactivity of dissolved trace metals (Cd,Cu, Ni) in surface waters from the Mississippi River to Gulf of Mexico

It is generally assumed that estuarine mixing is continuous for metals from terrestrial sources, gradually decreasing towards the open ocean endmember. Here we show that, chemical reactivity, determined by ion exchange method, and molecular weight distributions, obtained using cross-flow ultrafiltration, of dissolved Cd, Cu, and Ni in the surface waters of the Gulf of Mexico varied systematically across the estuarine mixing zone of the Mississippi River. Most size or chemical affinity fractions of dissolved metals (<0.4 μm) were linearly related to salinity (10.8–36.6), suggesting that the distribution of these elements was mainly controlled by continuous mixing processes. Dissolved concentrations across the salinity gradient ranged for Cd: 87–187 pM; Cu: 1.4–18.3 nM; and Ni: 2.6–18.8 nM, with highest values near the Mississippi river mouth, and lowest concentrations in a warm core ring in the Gulf of Mexico. Dissolved Cd was mostly present as a truly dissolved (<10 kDa, 97 ± 1%) and cationic fraction (Chelex-100 extractable, 94 ± 4%). A novel observation across the estuarine mixing zone was that colloidal metal concentrations were identical to either inert (for Cu, Ni) or AMPG-labile anionic (Cu, Cd) fractions. The difference in behavior between Cu and the other two metals might indicate differences in the biopolymeric nature of the metal–organic chelates. In particular, the anionic-organic Cd fractions accounted for just 3 ± 1%, on average. However, for Cu, it was 24 ± 4%, and for Ni, it was 9 ± 6%. The fractions of the total dissolved metal fractions that were “inert” averaged 31 ± 10% for Cu and 29 ± 12% for Ni. Small but noticeable amounts (6 ± 3%) of dissolved inert Cd fractions were also present. Apparent non-local transport processes, likely associated with cross-shelf sediment resuspension processes, could have been responsible for the relatively high concentrations of ‘inert’ and ‘anionic’ metal fractions in high salinity coastal waters, and accounting for the persistence of metals bound to humic substances in the Gulf of Mexico.     

Outflow of trace metals into the Laptev Sea by the Lena River

Freshwater concentrations confirm the pristine character of the Lena River environment as already pointed-out in a previous study with a limited set of data (Martin et al., 1993). Total dissolved concentrations of the freshwater are 13.8 ± 1.6 nM, Cu, 4.4 ± 0.1 nM, Ni, 0.054 ± 0.047 nM, Cd, 642 ± 208 nM, Fe, 0.2–0.3 nM Pb and 1.2 ± 1.0 nM, Zn. For Zn and Pb, a simple mixing of the Lena River waters with the Arctic waters is observed. Relationships with salinity suggest that for Cu, Ni and Cd, there is a mobilization of the dissolved fraction from the suspended matter, with an increase of the dissolved concentration of 1.5, 3 and 6 times, respectively. For Fe, the total dissolved concentrations follow an exponential decrease in the mixing zone and 80% of the total “dissolved” Fe is removed from the solution. For Cu, Ni, Cd and Fe, the riverine end-members are 20 nM, 12 nM, 0.3 nM and 47 nM, respectively. When considering the input of total dissolved metals to the Arctic Ocean, the fraction attributed to the freshwaters from the Arctic rivers appears to be small (4% of the input of dissolved metal to the Arctic Ocean for Cd, 27% for Cu, 11 % for Ni and 2% for Zn). Metal concentrations in the Laptev Sea and Arctic Ocean are very similar, indicating a generally homogeneous distribution in the areas sampled.     

Eutrophication and hypoxia in the upper Gulf of Thailand

In this study, we investigated the mechanism of eutrophication and hypoxia in the upper Gulf of Thailand from August 2014 to June 2015 based on field observation data, box model analysis, and the unscaled trophic status index (UNTRIX). Fresh water residence time derived from a simple box model was long (38.61 days) during the transition period between the southwest to northeast monsoon in September 2014. In contrast, fresh water residence time was short (2.63 days) during the late northeast monsoon in February 2015. Long residence time was related to the development of widespread strong hypoxia in near-bottom waters in over half of the gulf during the transition between the southwest and the northeast monsoon, when river discharge was also very large. UNTRIX is used to assess water trophic levels, and is based on water qualities including concentrations of chlorophyll-a (Chl-a), dissolved oxygen (DO), dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphorus (DIP). Hypertrophic and eutrophic conditions were observed at river mouths; their seasonal eutrophication was related to river discharge and circulation. Nutrients were mainly increased by river discharge. Water column stratification and long residence time were required for the development of severe hypoxia in the study area.

     

Hydrography, nutrients and chlorophyll during El Niño and La Niña 1997–99 winters in the Gulf of the Farallones, California

Nutrient and chlorophyll concentrations were measured in January 1997, 1998 and 1999 in the Gulf of the Farallones, CA at locations stretching north/south from Point Reyes to Half Moon Bay, and seaward from the Golden Gate to the Farallon Islands. The cruises were all carried out during periods of high river flow, but under different climatological conditions with 1997 conditions described as relatively typical or ‘neutral/normal’, compared to the El Niño warmer water temperatures in 1998, and the cooler La Niña conditions in 1999. Near-shore sea-surface temperatures ranged from cold (9.5–10.5°C) during La Niña 1999, to average (11–13°C) during 1997 to warm (13.5–15°C) during El Niño 1998. Nutrients are supplied to the Gulf of the Farallones both from San Francisco Bay (SFB) and from oceanic sources, e.g. coastal upwelling near Point Reyes. Nutrient supplies are strongly influenced by the seasonal cycle of fall calms, with storms (commencing in January), and the spring transition to high pressure and northerly upwelling favorable winds. The major effect of El Niño and La Niña climatic conditions was to modulate the relative contribution of SFB to nutrient concentrations in the coastal waters of the Gulf of the Farallones; this was intensified during the El Niño winter and reduced during La Niña. During January 1998 (El Niño) the oceanic water was warm and had low or undetectable nitrate, that did not reach the coast. Instead, SFB dominated the supply of nutrients to the coastal waters. Additionally, these data indicate that silicate may be a good tracker of SFB water. In January, delta outflow into SFB produces low salinity, high silicate, high nitrate water that exits the bay at the Golden Gate and is advected northward along the coast. This occurred in both 1997 and 1998. However during January 1999, a La Niña, this SFB feature was reduced and the near-shore water was more characteristic of high salinity oceanic water penetrated all the way to the coast and was cold (10°C) and nutrient rich (16 μM NO₃, 30 μM Si(OH)₄). January chlorophyll concentrations ranged from 1–1.5 μg l⁻¹ in all years with the highest values measured in 1999 (2.5–3 μg l⁻¹) as a result of elevated nutrients in the area. The impact of climatic conditions on chlorophyll concentrations was not as pronounced as might be expected from the high temperatures and low nutrient concentrations measured offshore during El Niño due to the sustained supply of nutrients from the Bay supporting continued primary production.