Search

The oxygen deficient mesopelagic layer (ODL) off Peru has concentrations below 5 μmol O2 kg–1 and is delimited by a shallow upper oxycline with strong vertical gradient and a more gradual lower oxycline (lOx). Some regions show a narrow band of slightly increased oxygen concentrations within the ODL, an intermediate oxygen layer (iO2). CTD, oxygen and lowered Acoustic Doppler Current Profiler (LADCP, 300 kHz) profiles were taken on the shelf edge and outside down to mostly 2000 m. We evaluate here the acoustic volume backscatter strength of the LADCP signal representing organisms of about 5 mm size. Dominant features of the backscatter profiles were a minimum backscatter strength within the ODL, and just below the lOx a marked backscatter increase reaching a maximum at less than 3.0 μmol O2 kg–1. Below this maximum, the acoustic backscatter strength gradually decreased down to 1000 m below the lOx. The backscatter strength also increased at the iO2 in parallel to the oxygen concentration perturbations marking the iO2. These stable backscatter features were independent of the time of day and the organisms represented by the backscatter had to be adapted to live in this microaerobic environment. During daylight, these stable structures were overlapped by migrating backscatter peaks. Outstanding features of the stable backscatter were that at very low oxygen concentrations, the volume backscatter was linearly related to the oxygen concentration, reaching half peak maximum at less than 2.0 μmol O2 kg–1 below the lOx, and the depth-integrated backscatter of the peak below the lOx was higher than the integral above the Ox. Both features suggest that sufficient organic material produced at the surface reaches to below the ODL to sustain the major fraction of the volume backscatter-producing organisms in the water column. These organisms are adapted to the microaerobic environment so they can position themselves close to the lower oxycline to take advantage of the organic particles sinking out of the ODL.

Prolonged nitrogen (N) fertilization can impact seagrass survival and productivity; however, the effects of N enrichment pulses (e.g., upwelling or sediment resuspension) remain poorly understood. This study examined the effects of short-term (1 h) pulsing of nitrate (NO3−) enrichment, simulating an upwelling event, on dissolved inorganic carbon (DIC) and NO3− uptake capacities, critical in controlling eelgrass productivity. Zostera marina dominates submerged vegetation in coastal lagoons influenced by upwelling in the California Current system. Laboratory incubations were conducted in winter (non-upwelling) and spring (upwelling) with shoots collected from San Quintin Bay meadows, Baja California, Mexico, differentially exposed to upwelled NO3−. Results suggest that NO3− enrichment stimulated DIC and NO3− uptake in winter, reflecting the close relationship between carbon metabolism and NO3− assimilation. Eelgrass shoots showed reduced NO3− incorporation in spring; neither NO3− uptake nor photosynthesis increased when exposed to high NO3−. Saturation of spring shoots at lower ambient NO3− concentrations may be interpreted as a physiological strategy to restrict metabolically costly NO3− incorporation during upwelling; this regulation of NO3− uptake strongly contrasts to the apparently full exploitation of this nutrient by seaweeds also dominant within the bay, as indicated in previous works. Despite their reduced NO3− uptake, eelgrass meadows near the bay mouth acquire NO3− at rates up to 4.2 mmol N m−2 day−1. This represents non-trivial water column NO3− removal compared to the estimated oceanic NO3− supply (~ 7.1 mmol m−2 day−1) during upwelling, highlighting the importance of Z. marina beds in controlling the lagoonal N-budget.

Highlights: • The epoch of the Anthropocene, a period during which human activity has been the dominant influence on climate and the environment, has witnessed a decline in oxygen concentrations and an expansion of oxygen-depleted environments in both coastal and open ocean systems since the middle of the 20th century. • This review paper provides a synthesis of system-specific drivers of low oxygen in a range of case studies representing marine systems in the open ocean, on continental shelves, in enclosed seas and in the coastal environment. • Identification of similar and contrasting responses within and across system types and corresponding oxygen regimes is shown to be informative both in understanding and isolating key controlling processes and provides a sound basis for predicting change under anticipated future conditions. • Case studies were selected to achieve a balance in system diversity and global coverage. • Each case study describes system attributes, including the present-day oxygen environment and known trends in oxygen concentrations over time. • Central to each case study is the identification of the physical and biogeochemical processes that determine oxygen concentrations through the tradeoff between ventilation and respiration. • Spatial distributions of oxygen and time series of oxygen data provide the opportunity to identify trends in oxygen availability and have allowed various drivers of low oxygen to be distinguished through correlative and causative relationships. • Deoxygenation results from a complex interplay of hydrographic and biogeochemical processes and the superposition of these processes, some additive and others subtractive, makes attribution to any particular driver challenging. • System-specific models are therefore required to achieve a quantitative understanding of these processes and of the feedbacks between processes at varying scales. Abstract: The epoch of the Anthropocene, a period during which human activity has been the dominant influence on climate and the environment, has witnessed a decline in oxygen concentrations and an expansion of oxygen-depleted environments in both coastal and open ocean systems since the middle of the 20th century. This paper provides a review of system-specific drivers of low oxygen in a range of case studies representing marine systems in the open ocean, on continental shelves, in enclosed seas and in the coastal environment. Identification of similar and contrasting responses within and across system types and corresponding oxygen regimes is shown to be informative both in understanding and isolating key controlling processes and provides a sound basis for predicting change under anticipated future conditions. Case studies were selected to achieve a balance in system diversity and global coverage. Each case study describes system attributes, including the present-day oxygen environment and known trends in oxygen concentrations over time. Central to each case study is the identification of the physical and biogeochemical processes that determine oxygen concentrations through the tradeoff between ventilation and respiration. Spatial distributions of oxygen and time series of oxygen data provide the opportunity to identify trends in oxygen availability and have allowed various drivers of low oxygen to be distinguished through correlative and causative relationships. Deoxygenation results from a complex interplay of hydrographic and biogeochemical processes and the superposition of these processes, some additive and others subtractive, makes attribution to any particular driver challenging. System-specific models are therefore required to achieve a quantitative understanding of these processes and of the feedbacks between processes at varying scales.

Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO2 (pCO2) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions within and among margins., Anthropogenic CO2 is acidifying the ocean, but knowledge of the carbonate properties underlying these dynamics in coastal oceans is lacking. Here, the authors reveal spatial distribution patterns and variability in carbonate chemistry along North America’s coasts.

In the Gulf of Mexico (GoM), the upper 300 m of the water column contains a mixture of water types derived from water masses from the North Atlantic and the Caribbean Sea, namely Caribbean Surface Water (CSW), Subtropical Underwater (SUW), Gulf Common Water (GCW), and Tropical Atlantic Central Water (TACW). These are mainly altered by mesoscale processes and local evaporation, which modulate biogeochemical cycles. In this study, we improve our understanding of water mass dynamics by including biogeochemical data when evaluating the T-S relationship to define water-mass boundaries, particularly when the observed thermohaline characteristics overlap. The variables considered were apparent oxygen utilization (AOU), nitrate, and dissolved inorganic carbon (DIC). The data were obtained from eight cruises carried out in the central and southern regions of the GoM and an additional cruise that covered the entire coastal-ocean region. The new proposed boundaries were instrumental in clarifying the dynamics of surface waters. Of note, GCW on the western side of the GoM is not formed from the mixing of CSW and SUW but by the mixing of remnant CSW with TACW. In winter, a remnant of CSW mixed with GCW, and the biogeochemical composition of surface waters was affected, as observed from an increase in nitrate and DIC concentrations and positive AOU values. CSW was mainly detected at the surface during summer with negative AOU values, low DIC values, and almost undetectable nitrate concentrations. The presence or absence of CSW modulated the depth of the nitracline and likely influenced primary productivity.

Seasonal variations of the CO2 system in seawater for coral reefs are often controlled by both chemical-biological processes and by regional oceanographic features in combination with the residence time of adjacent water. This study reports the seasonal variability of the CO2 system along a year though dissolved inorganic carbon and pH measurements in Cabo Pulmo, a fringing reef from the Mexican Pacific. Two conditions were found on the reef: summer with the presence of Tropical Surface Water (TSW), characterized by high temperature, lower DIC levels, and a higher aragonite saturation (Ωarag); and winter with Gulf of California Water (GCW), when the opposite occurred. This seasonal variation was due to the horizontal advection of two surface water masses: Gulf of California water during winter and Tropical Surface Water the rest of the year as a result of the ocean circulation at the entrance of the Gulf of California. Therefore, the reef is significantly influenced by open ocean waters, where the depth is less than 20 m. The seasonal variability in Ωarag between months with the presence of GCW and TSW is one of the largest ranges reported in coral reefs (ΔΩarag = 0.5 units). Our results suggest that the reef community cannot modify the aragonite or pH of incoming ocean water. This might be the case in other fringing reefs, where the use of ocean acidification forecast models is suitable.

In the Gulf of Mexico (GoM) at least three near-surface water masses are affected by mesoscale processes that modulate the biogeochemical cycles. Prior studies have presented different classifications of water masses where the greater emphasis was on deep waters and not on the surface waters (σθ −3), as in this work. Here presents a new classification of water masses in the GoM, based on thermohaline properties and dissolved oxygen (DO) concentration using data from a total of five summer and winter cruises carried out primarily in the central GoM. The reclassification includes an adjustment to the spatial range of Caribbean Surface Water (CSW), which is detected only during the summer. This water mass extends from the surface to ≈ 90 m and features warm waters (27–32 °C), high salinities (up to ≈ 36.8), non-detectable nitrate concentration, and negative values of the apparent oxygen utilization (AOU) of ≈ −27 μmol kg−1. Below the CSW, the deeper Gulf Common Water (GCW) was also redefined and characterized by a subsurface DO maximum, with values ≈ 50 μmol kg−1 higher than that found in surface waters. In winter, a replacement of the CSW by the GCW affected the biogeochemical composition of surface water as observed from an increase in nitrate concentrations, positives values of AOU (≈ 90 μmol kg−1) and a decrease in surface temperatures (Nortes season. CARS2009 analysis supports the formation of the subsurface maximum of DO during the summer and disappears in winter. In this work also named surface water that is characterized by a low salt content (≈ 33.1) from 0 to 20 m as Freshwater Influenced Surface Water (FISW).

As a result of anthropogenic activities, it has been predicted that the ocean will be challenged with rising temperature, increased stratification, ocean acidification, stronger more frequent tropical storms, and oxygen depletion. In the tropical Pacific off central Mexico all these phenomena are already occurring naturally, providing a laboratory from which to explore ocean biogeochemical dynamics that are predicted under future anthropogenic forcing conditions. Here, seasonally anomalous surface tropical waters were detected as a result of the developing "Godzilla El Nino 2015-2016". The incursion of this oxygenated water modified the local structure of an intense and shallow oxygen minimum zone, partially eroding and intensifying the oxycline while having an associated impact on the carbon maximum zone. The core of the oxygen minimum zone (

The dynamics of the Loop Current (LC) and the detached Loop Current eddies (LCEs) dominate the surface circulation of the Gulf of Mexico (GoM) and transport Caribbean Water (CW) into the gulf. In this work, 25 years (1993–2017) of daily satellite data are used to investigate the variability of these physical processes and their effect on chlorophyll a (Chl a) concentrations from 1998 to 2017, including temporal changes, mean differences, and regional concentration tendencies. The physical variables analyzed are absolute dynamic topography (ADT) and oceanic currents. From the ADT and oceanic current monthly climatologies, it is shown that there is an annual intrusion of CW with an inward incursion that starts in spring, peaks in the summer, reaches to 28∘ N and 90.45∘ W, and then retreats in winter to approximately 26.5 ∘ N and 88.3 ∘ W. Minimum surface Chl a concentrations (−3) are found during the summer–autumn period inside the region of maximum incursion of CW; the opposite is observed during the winter period when Chl a concentrations were at a maximum, e.g., > 0.14 mg m−3. The 3-year running averages of the ADT 40 cm isoline qualitatively reproduce the climatological pattern of 25 years showing that before 2002 CW was less intrusive. This suggests that from 2003 onward, larger volumes of oligotrophic waters from the Caribbean Sea have invaded the western GoM and reduced mean surface Chl a concentrations. A direct comparison between the 1998–2002 and 2009–2014 periods indicates that in the latter time interval, the Chl a concentration above waters deeper than 250 m has decreased significantly.

The surface of the ocean has absorbed one-third of the CO2gas that has been released by anthropogenic activities, which has resulted in a reduction in pH and the aragonite saturation state (Ωara) with potential negative impacts in calcifying organisms, such as corals. To evaluate these effects, the natural variability present must first be understood, including that of processes that operate at diurnal, seasonal, and interannual frequencies. The objective of this study was to determine the influence of physical and biogeochemical processes on the seasonal variability of the CO2-system in a fringe coral reef of the Eastern Tropical Pacific (ETP). To achieve this, a SeapHOx sensor was installed to measure temperature, salinity, dissolved oxygen, and pHTot at 30-min intervals from November 2013 (early winter) to July 2014 (early summer). The recorded temperature and salinity data fed a mixing model to identify the water masses present in the reef. We show how physical and biogeochemical oceanic processes influence and control the variability of the carbonate system. The presence of water masses with different carbon chemistries responded to two scenarios: (1) seasonal circulation on the order of months and (2) an intermittence between water masses related to mesoscale structures (eddies) on the order of weeks. A low-pH and Ωara condition was detected during summer, which was related to the presence of warm and respired Tropical Surface Water. The broadest changes in Ωara were the result of physical processes (winter ΔΩara = 0.14 and summer ΔΩara = 0.34 units) and corresponded to the transition between water masses with different carbon-biogeochemistry signals. Our results suggest that the Cabo Pulmo coral community develops in an environment with a wide range of pH and Ωara conditions and that seasonal changes are controlled by open ocean carbon biogeochemistry.

Porites panamensis is a hermatypic coral present in the eastern Pacific Ocean. Skeletal growth parameters have been reported, but studies of the relationship between annual calcification rates and environmental controls are scarce. In this study, we investigated three aspects of the annual calcification rates of P. panamensis: growth parameters among three P. panamensis populations; the sea surface temperature as a calcification rate control spanning a latitudinal gradient; and calcium carbonate production among three sites. Growth parameters varied among the sites due to the colony growth form. Massive colonies in the north showed a higher calcification rate than encrusting colonies in the south (mean: 1.22–0.49 g CaCO3 · cm−2 · yr−1), where variations in calcification rates were related to growth rate (0.91–0.38 cm · yr−1) rather than to skeletal density differences (overall mean ± SD, 1.31 ± 0.04 g CaCO3 · cm−3). Our results showed a positive linear relationship between annual calcification rates and sea surface temperatures within these P. panamensis populations. Differences were related to distinct oceanographic environments (within and at the entrance of the Gulf of California) with different sea surface temperature regimes and other chemical properties. Different populations calcified under different environmental conditions. Calcium carbonate production was dependent upon the calcification rate and coral cover and so carbonate production was higher in the north (coral cover 12%) than in the south (coral cover 3.5). Thus, the studied sites showed low calcium carbonate production (0.25–0.43 kg CaCO3 · m−2 · yr−1). Our results showed reduced calcification rates, regional temperature regime control over calcification rates, different growth forms, low coral cover and low calcium carbonate production rates in P. panamensis.

Ocean acidification is widely accepted as a primary threat to coral reef populations. Negative physiological effects include decreased calcification rates, heightened metabolic energy expenditure, and increased dissolution of coral skeletons. However, studies on the dissolution of coral skeletons structures under ocean acidification conditions and their implications on sediments remain scarce. In this work, we examined skeletal dissolution kinetics from four of the most representative hermatypic corals of the Eastern Pacific coasts (Pocillopora, Porites, Pavona, and Psammocora). Samples were treated with a highly acidic solution for defined periods of time, and measurements of dissolved calcium ([Ca+2]) were used to evaluate the kinetics of coral skeleton dissolution. All genera tests except Porites showed a zero reaction rate. Porites exhibited a first-order reaction and a faster reaction rate than other genera. Compression strength tests and skeletal density did not correlate with reaction rate. Pavona showed greater structural strength. Porites were the most susceptible to acidic dissolution compared to other genera tested due to their morphology, i.e., possession of the largest surface area, suggesting a high vulnerability under low-pH conditions. The hierarchical response in dissolution kinetics among coral genera tested suggests that the most soluble coral might act as a buffer under ocean acidification conditions.

Three oceanographic cruises were carried out in the region of the Ballenas Channel (BC) during winter 2002, spring 2003, and summer 2004, in order to study the impact of vertical mixing of the water column (o) on the surface concentration of dissolved inorganic nutrients (NO3, PO4, and Si(OH)4). Mean nutrient concentrations integrated over the upper 100 m of BC showed a clear seasonal variation, with higher values in winter (18.2 ± 1.1 ± µM NO3, 2.36 ± 0.08 µM PO4, and 35.4 ± 3.2 µM Si(OH)4), associated with a well-mixed water column (o = 0.7–16 J m–3), and low values in summer (7.1 ± 1.0 µM NO3, 1.22 ± 0.06 µM PO4, and 16.0 ± 2.1 µM Si(OH)4), related to vertically stratified water column conditions (o = 150–223 J m–3). In contrast, below 200 m the seasonal variability of the three nutrient concentrations was reduced. The hydrographic analysis indicated that the wintertime surface nutrient enrichment was due to an intensification of the water column mixing, which vertically transported Subtropical Subsurface Water (SSW, cold and nutrient-enriched) to the surface of BC. In contrast, nutrient impoverishment in summertime was due to biological consumption combined with the stratification of the water column, which reduced the vertical flow of SSW and, consequently, the supply of nutrients to the surface of this system. The N:P and Si:N ratios and an excess of PO4 > 0.65 M in surface waters indicated that NO3 was the potential limiting nutrient for primary production in this oceanographic province of the Gulf of California. Se realizaron tres cruceros oceanograficos en la region del canal de Ballenas (CB) durante el invierno de 2002, la primavera de 2003 y el verano de 2004, con el objetivo de estudiar el impacto de la mezcla vertical de la columna de agua (o) sobre la concentracion superficial de los nutrientes inorganicos disueltos (NO3, PO4 y Si(OH)4). Las concentraciones promedio de nutrientes integrados en los primeros 100 m del CB mostraron una clara variacion estacional, con valores altos en el invierno (18.2 ± 1.1 µM de NO3, 2.36 ± 0.08µM de PO4 y 35.4 ± 3.2 µM de Si(OH)4), asociados a condiciones de mezcla intensa de la columna de agua (o = 0.7–16 J m–3), y valores bajos en el verano (7.1 ± 1.0 µM de NO3, 1.22 ± 0.06 µM de PO4 y 16.0 ± 2.1 µM de Si(OH)4), asociados a condiciones de estratificacion de la columna de agua (Φ = 150–223 J m–3). En contraste, por debajo de los 200 m la variabilidad estacional de la concentracion de los tres nutrientes fue muy pequena. El analisis hidrografico indico que el enriquecimiento superficial de nutrientes en invierno se debio a la intensificacion de la mezcla de la columna de agua, la cual transporto verticalmente el Agua Subsuperficial Subtropical (ASS, fria y rica en nutrientes) hacia la superficie del CB. En contraste, el empobrecimiento de nutrientes durante el verano se debio a que el consumo por la actividad biologica se combino con la estratificacion de la columna de agua, la cual redujo el flujo vertical del ASS y, en consecuencia, el aporte de nutrientes hacia la superficie de este sistema. Las razones N:P, Si:N y un exceso de PO4 > 0.65 M en las aguas superficiales indicaron que el NO3 fue el nutriente potencialmente limitante para la produccion primaria de esta provincia oceanografica del golfo de California.

In the Midriff Islands region (MIR) of the Gulf of California (Mexico), tidal mixing plays a very important role in the distribution of chemical properties. Although the temporal variability of the water masses is linked to the ocean dynamics of this region, its importance has not been considered. This work estimates the effect of water mass dynamics on the spatial distribution and seasonal variation of dissolved inorganic carbon (DIC) in the region, with special emphasis on the Ballenas Channel, during winter 2002, spring 2003, and summer 2004. Gulf of California Water (GCW) was found throughout the area in the first 100 m. Below, Subtropical Subsurface Water (SSW) filled the Delfín, Salsipuedes, and Tiburón basins, while to the southeast it was found between 150 and 350 m. Pacific Intermediate Water did not cross the sills. SSW enriches the surface water of the MIR with DIC when it increases in volume and when mixed with GCW by tidal effects. This contribution decreases towards summertime, when SSW sinks and the volume of GCW increases. In winter, GCW had three water types associated with oceanographic mixing processes and in combination with the presence of SSW. There was a strong DIC vs temperature relationship, which can be applied to analyze the carbon dynamics in the MIR, both at the surface using satellite imagery and vertically to simulate physical processes.

The role of coastal lagoons and estuaries as sources or sinks of inorganic carbon in upwelling areas has not been fully understood. During the months of May–July, 2005, we studied the dissolved inorganic carbon system in a coastal lagoon of northwestern Mexico during the strongest period of upwelling events. Along the bay, different scenarios were observed for the distributions of pH, dissolved inorganic carbon (DIC) and apparent oxygen utilization (AOU) as a result of different combinations of upwelling intensity and tidal amplitude. DIC concentrations in the outer part of the bay were controlled by mixing processes. At the inner part of the bay DIC was as low as 1800 μmol kg −1 , most likely due to high water residence times and seagrass CO 2 uptake. It is estimated that 85% of San Quintin Bay, at the oceanic end, acted as a source of CO 2 to the atmosphere due to the inflow of CO 2 -rich upwelled waters from the neighboring ocean with high positive fluxes higher than 30 mmol C m −2 d −1 . In contrast, there was a net uptake of CO 2 and HCO 3 − by the seagrass bed Zostera marina in the inner part of the bay, so the p CO 2 in this zone was below the equilibrium value and slightly negative CO 2 fluxes of −6 mmol C m −2 d −1 . Our positive NEP and ΔDIC values indicate that Bahia San Quintin was a net autotrophic system during the upwelling season during 2005.

The temporal variability of the physical and chemical conditions of coastal waters off Ensenada, Baja California (Mexico) was characterized. A historical analysis was made based on 11 years (1998–2008) of temperature and salinity data records measured quarterly by IMECOCAL, along a transect perpendicular to the coast (CalCOFI line 100). Moreover, the physical and chemical conditions at a coastal monitoring observatory called station ENSENADA were described using a 2-year data series (October 2006–November 2008) obtained with improved temporal resolution. The historical analysis of line 100 showed marked seasonal variability in the thermohaline conditions associated with fluctuations in the flow of the equatorward California Current and the poleward California Undercurrent, as well as with coastal upwelling events whose magnitude and frequency increase towards spring–summer. Interannual variability was also observed, related to warm and/or cold ENSO phases that modify the characteristics of the water column in this coastal region. The most striking characteristics of the interannual variability at station ENSENADA were La Nina conditions recorded from summer 2007 to mid 2008. During this cold ENSO phase, temperature, salinity, dissolved oxygen, density, and dissolved inorganic carbon data revealed the anomalous presence of subsurface water at the surface layers in spring 2008. Results suggest that the coastal observatory is sensitive to the temporal variability of hydrographic conditions on shelf coastal waters (

The temporal and spatial variability of dissolved inorganic phosphate (DIP), nitrogen (DIN), carbon (DIC) and dissolved organic carbon (DOC) were studied in order to determine the net ecosystem metabolism (NEM) of San Diego Bay (SDB), a Mediterranean-climate lagoon. A series of four sampling campaigns were carried out during the rainy (January 2000) and the dry (August 2000 and May and September 2001) seasons. During the dry season, temperature, salinity and DIP, DIC and DOC concentrations increased from oceanic values in the outer bay to higher values at the innermost end of the bay. DIP, DIC and DOC concentrations showed a clear offset from conservative mixing implying production of these dissolved materials inside the bay. During the rainy season, DIP and DOC increased to the head, whereas salinity decreased toward the mouth due to land runoff and river discharges. The distributions of DIP and DOC also showed a deviation from conservative mixing in this season, implying a net addition of these dissolved materials during estuarine mixing within the bay. Mass balance calculations showed that SDB consistently exported DIP (2.8–9.8 × 10 3 mol P d −1 ), DIC (263–352 × 10 3 mol C d −1 ) and DOC (198–1233 × 10 3 mol C d −1 ), whereas DIN (5.5–18.2 × 10 3 mol N d −1 ) was exported in all samplings except in May 2001 when it was imported (8.6 × 10 3 mol N d −1 ). The DIP, DIC and DOC export rates along with the strong relationship between DIP, DIC or DOC and salinity suggest that intense tidal mixing plays an important role in controlling their distributions and that SDB is a source of nutrients and DOC to the Southern California Bight. Furthermore, NEM ranged from −8.1 ± 1.8 mmol C m −2 d −1 in September to −13.5 ± 5.8 mmol C m −2 d −1 in January, highlighting the heterotrophic character of SDB. In order to explain the net heterotrophy of this system, we postulate that phytoplankton-derived particulate organic matter, stimulated by upwelling processes in the adjacent coastal waters, is transported into the bay, retained and then remineralized within the system. Our results were compared with those reported for the heterotrophic hypersaline coastal lagoons located in the semi-arid coast of California–Baja California, and with those autotrophic hypersaline systems found in the semi-arid areas of Australia. We point out that the balance between autotrophy and heterotrophy in inverse estuaries is dependent on net external inputs of either inorganic nutrients or organic matter as it has been indicated for positive estuaries.

Rhodolith beds are the dominant submerged calcifying aquatic vegetation in some coastal marine environments worldwide but few quantitative data are available regarding their physiology. In the Gulf of California (Mexico), Lithophyllum margaritae (Rhodophyta, Corallinaceae) is the most abundant nongeniculate, rhodolith-forming coralline species. Over their gulf-wide distribution, rhodoliths are exposed to a wide range of seasonal temperatures (~8–32ºC). The effect of changes in temperature on the photosynthetic and calcification rates of this species is unknown. We therefore evaluated the effect of temperature (10–30ºC) on the photosynthetic and calcification rates of L. margaritae rhodoliths in the lab and examined the effect of seasonal changes in temperature on growth rates in the field. Photosynthetic rates were evaluated polarographically and calcification rates were evaluated in the lab using both the buoyant weight technique and total alkalinity method, and in the field through alizarin staining. To the best of our knowledge, this is the first time that these three methods are used simultaneously to evaluate growth rates in coralline algae. Photosynthetic, calcification and growth rates showed wide fluctuations as a result of laboratory or field temperature. Photosynthetic (Pmax) and respiratory rates both increased five-fold as incubation temperature increased to 25–30ºC. Similarly, calcification rates in the lab and growth rates in the field increased with higher temperatures. The lab data suggest that rhodolith growth is seasonally regulated by seawater temperature. The buoyant weight and total alkalinity techniques for determining calcification rate were comparable at low temperatures, but variability increased with temperature and this will be examined in further studies. Field growth rates, presented as apical tip extension, were significantly higher in summer (5.02 ± 1.16 mm yr–1) than in winter (0.83 ± 0.16 mm yr–1), supporting the lab results. The strong effects of temperature on photosynthetic, calcification and growth rates of Lithophyllum margaritae in the Gulf of California suggest that changes in sea surface temperature directly regulate bed production.

The temporal variation in the abundance and species composition of penaeid shrimp postlarvae and juveniles was studied in a tidal channel of the Colorado River estuary. Biweekly sampling during flood and ebb tide was conducted from March through November 2000. Postlarvae of the blue shrimp, Litopenaeus stylirostris, were observed beginning in May, with highest densities in early June during flood tide. A much smaller peak in densities occurred in late September, with few postlarvae found in October and November. Juvenile L. stylirostris were present in highest densities during ebb tide in mid-June, with smaller peaks in mid-July and late September. Densities of postlarval and juvenile brown shrimp, Farfantepenaeus californiensis, were much lower than those of L. stylirostris and without clearly defined peaks. The growth rate of juvenile L. stylirostris appeared similar to rates (30–60 mm month–1) reported for penaeid shrimp from the Pacific Ocean, Gulf of Mexico, and Australia. Management decisions affecting the Upper Gulf of California and Colorado River Delta Biosphere Reserve need to be cognizant of the importance of May and June as critical months in the use of the estuarine tidal channels by these commercially important species.

A cruise was conducted along the northwestern coast of Baja California, off the US-Mexico border region, to determine the physical, biological and anthropogenic factors affecting the concentration and distribution of phosphates (PO43–). The vertical distribution of temperature and PO43– showed isograms (13ºC and 0.75 µM, respectively) rising towards the shore. Although this phenomenon was observed in all the study area, it was more abrupt in the southern part than in the northern, resulting in lower phosphate concentrations in the north (0.50 µM) associated with high chlorophyll a concentrations (10.0 mg m–3). A principal components analysis indicated that the PO43– concentrations were related to upwelling (51%) and phytoplankton biomass (23%). A PO43– mass balance indicated that sewage discharge had a very local effect, contributing 3.0 ± 0.12 t d–1 (5%), while horizontal advection contributed 20.0 ± 2.2 t d–1 (32%) and upwelling supply was 41.1 ± 2.3 t d–1 (63%). If the PO43– sewage contribution trend does not change, we predict that in 2035 the anthropogenic contribution will be as high as the amount delivered to the area by the Californian Current. Conversely, if Mexico´ s sewage treatment systems improve to a level similar to that in the USA, we estimate that by 2012 the anthropogenic sources will be insignificant.

Nutrients (NO3 + NO2, PO4) and total organic carbon (TOC) from Estero de Punta Banda, a coastal lagoon of Baja California (Mexico), were studied during the 1992–93 El Niño. Samples were collected at four sites distributed along the main channel of the lagoon, during four different tidal stages. According to reports in the literature, this coastal lagoon behaves as an antiestuary most of the time, with salinity increasing significantly from the mouth inwards. Greater input of fresh water due to a larger rainfall, well above the annual mean (393 mm), caused the Estero to behave as an estuary, with salinity values of

Coastal environments are an important component of the global carbon cycle, and probably more vulnerable than the open ocean to anthropogenic forcings. Due to strong spatial heterogeneity and temporal variability, carbon flows in coastal environments are poorly constrained. Hence, an integrated, international, and interdisciplinary program of ship-based hydrography, Voluntary Observing Ship (VOS) lines, time-series moorings, floats, gliders, and autonomous surface vessels with sensors for pCO2 and ancillary variables are recommended to better understand present day carbon cycle dynamics, quantify air-sea CO2 fluxes, and determine future long-term trends of CO2 in response to global change forcings (changes in river inputs, in the hydrological cycle, in circulation, sea-ice retreat, expanding oxygen minimum zones, ocean acidification, ?) in the coastal oceans. Integration at the international level is also required for data archiving, management, and synthesis that will require multi-scale approaches including the development of biogeochemical models and use of remotely sensed parameters. The total cost of these observational efforts is estimated at about 50 million US dollars per year.

Se estudió la dinámica de nutrientes (NO3 + NO2 y PO4) y carbón orgánico total (COT) en el Estero de Punta Banda, Baja California (México), durante El Niño 1992–93. Se recolectaron muestras de agua superficial en cuatro localidades distribuidas a lo largo de la laguna, considerando cuatro estados diferentes de marea. De acuerdo con lo informado en la literatura, la mayor parte del tiempo esta laguna costera se comporta claramente como un antiestuario, con la salinidad aumentando significativamente de la boca hacia el interior. El incremento del aporte de agua dulce debido a la precipitación pluvial muy por encima de la media anual durante este evento (393 mm), causó que el Estero se comportara como estuario, con valores de salinidad menores que 25 y con un incremento de NO3 + NO2, PO4 y COT. Los valores de PO4 fluctuaron entre 0.5 y 3.5 µM y los de COT entre 2.3 y 9.8 mg L-1, con una clara tendencia a incrementarse de la boca hacia el interior de la laguna. Los valores de NO3 fluctuaron entre 0.2 y 2.3 µM en septiembre de 1992 y entre 1.4 y 6.8 µM en marzo de 1993, también con una clara tendencia a aumentar hacia el extremo interno de la laguna en el segundo caso. PO4 presentó una correlación negativa significativa (P 0.05) con la salinidad en marzo de 1993. La transformación de esta laguna costera de antiestuarina a estuarina por periodos prolongados, de hasta casi un año, está relacionada con eventos meteorológicos regionales, influenciados por fenómenos de gran escala como El Niño.

The environmental changes due to the Colorado River damming, have affected the ecological functioning of the nursery river delta and consequently the population of fishermen that live of the natural marine resources of the upper Gulf of California. We propose the use of urban wastewaters as a source of nutrients to fertilize the estuary, increase the primary productivity and therefore increase the population size of the estuarine dependent species, which are important for the fisheries in the region. In this way, we could partially restore the delta's ecological functioning and thus solve environmental, social, and economic problems. With a wastewater flow of 800 l·s-1 from “Las Arenitas” treatment plant, we could increase the primary organic productivity and ~1000 metric tons (mT) of shrimp landings of the region. These calculations are just for one fishery, but in a magnitude that could also increase in others.

El carbono es un elemento esencial en el planeta, que se involucra en procesos de gran escala como el calentamiento global, debido al aumento de gases de efecto invernadero en la atmósfera como el CO2; e incluso en procesos bioquímicos tan fundamentales para la vida como la fotosíntesis o la respiración. Debido a que posee un ciclo biogeoquímico gaseoso, es difícil entender las interacciones que se presentan en todo el conjunto del sistema terrestre-atmósfera-océano. Este último es el componente con mayor capacidad de almacén de carbono y se considera el mayor reservorio del planeta, con importantes variaciones en las zonas costeras. En la región frente al norte de Sinaloa, se presentan procesos físicos de mesoescala que propician una zona altamente productiva; región en la cual no hay estudios suficientes para conocer la dinámica del ciclo del carbono. El objetivo de este trabajo fue determinar la variabilidad estacional del sistema de carbono en un sitio de monitoreo con influencia de surgencias al norte de Sinaloa. Se realizaron tres muestreos (dos a bordo de B/O de la Secretaría de Marina) en la zona de surgencias frente al norte de Sinaloa; en septiembre 2016 (verano), en marzo 2017 (invierno) consideradas épocas contrastantes en la región y en junio 2017 (época de transición). Con un CTD, se realizaron perfiles verticales de temperatura, salinidad, oxígeno y clorofila, hasta 200 m de profundidad; también se tomaron alícuotas de profundidades estándar para determinar carbono inorgánico disuelto (CID), alcalinidad total (AT), pH, así como la concentración de clorofila. Mediante el programa CO2Sys se calculó el estado de saturación de aragonita (Ωaragonita). El estudio se complementó con imágenes de satélite de temperatura superficial del mar (TSM), clorofila (CLA), y Anomalías de la Altura del Nivel del Mar (SSHA). Los resultados obtenidos permitieron identificar en marzo 2017 (invierno) la presencia débil de surgencias que no influyeron de manera significativa en las variables del sistema de carbono; las cuales estuvieron influenciadas por un flujo somero de Agua Subtropical Subsuperficial (AStSs) proveniente del norte del golfo de California, la cual enriqueció de CID [˃ 2100 µmol kg-1] las aguas superficiales. En general, el sistema de carbono en esta zona de estudio presentó variabilidad debida a procesos físicos como mezcla vertical, advección horizontal, la presencia de remolinos anticiclónicos y por la variabilidad y estacionalidad de las masas de agua presentes en la zona. El AStSs fue la masa de agua que presentó la mayor concentración de CID ˃ 2100 µmol kg-1 Tesis