Thermohaline Conditions Research Articles

Small-scale energy potential from salinity gradients at a transboundary riverine estuary in the Yucatán Peninsula

This study estimates the environmental and technical energy potential of the thermohaline conditions in the Mexico–Belize riverine estuary. Site-specific conditions were considered based on monthly water temperature, salinity, and river discharge field measurements along the Hondo River estuary from 2018 to 2019. The practical extractable energy assessment described the possibility of outlining a hypothetical ∼3 MW salinity gradient energy (SGE) plant, which could support 5.4–15.1% of houses in the main urbanised area. Low-income housing benefits can be viable for up to 7700 houses with either mechanical or natural ventilation under tropical weather conditions. Alternatively, this energy may be directed towards commercial shared zones between Mexico and Belize. SGE harnessing might be possible throughout the year with limited zero extraction periods provided by seasonal thermohaline variations in the estuary during the dry season and at mid-summer droughts. The energy potential of the Hondo River was compared with manatee presence to explore possible environmental implications from SGE harnessing. The periods of high energy potential were followed by peaks in manatee sightings with a 1–2-month delay. The SGE approach based on a small-scale energy-generation scheme for the local coastal urbanised area considering the binational framework is discussed. • Small estuarine systems may contribute to local or remote energy consumption. •Salinity gradient energy (SGE) is suitable for local small-scale energy-generation. •A hypothetical 3 MW SGE-plant is outlined for the Mexico–Belize riverine estuary. •Benefits are feasible for 7700 low-income houses under tropical weather conditions. •Peaks of high SGE potential and flagship specie sightings present a 1–2-month lag.

AARI Modern Oceanographic Researches in the Arctic and Their Main Results

The article briefly highlights the main results of the activities in the field of studying the waters of the Arctic Ocean and the Arctic seas over a period covering the last decade. Information about the most significant expeditions carried out in the high-latitude Arctic after the International Polar Year 2007/08 and large summaries of the obser- vation results are given. Attention is drawn to the preservation and deepening of trends in changes in thermohaline conditions in the water area of the high-latitude Arctic seas.

Formation of dense water dome over the Central Bank under conditions of reduced ice cover in the Barents Sea

In this study on the basis of various data sets we traced formation of a ‘dome’- shaped density structure over the Central Bank - an important morphological element of the Barents Sea bottom topography. The major conclusion, which follows from the performed analysis, is that under changed conditions at the sea surface, transformation of thermohaline structure during the cold season principally differs from that under the mean climate conditions in the 20th century. Transition from the stratified vertical structure (in summer) to the homogeneous one (in winter) is governed by thermal convection. Additional input of warm and salty water with inflowing Atlantic origin water is crucial to allow vertical mixing to reach the seabed before the temperature drops to the freezing point. Cascading of dense water from the bank commences as soon as the convection goes down to the level of seabed. The influence of cascading on the Barents Sea hydrographic structure extends several hundreds of kilometers off the bank. In the absence of advective influx of salt and warm water vertical convection can also reach the seabed. However, under this condition formation of sea ice and haline convection is required. In this case water temperature in the homogeneous water column over the bank is close to the freezing point. Obtained results suggest that in the warmer climate the role of sea ice in winter transformation of thermohaline conditions over the bank is opposite to what it was in the 20th century: imported sea ice blocks convection, thus making the water in the dense ‘dome’ warmer than it typically was in colder climate.

Thermohaline conditions and circulation in the Gulf of Thailand during the northeast monsoon

Hydrographic data from the Gulf of Thailand (GoT) reveal two bottom saline water areas (BSWA1 and BSWA2) with salinity (S) ≥ 33.0 psu and where the water columns are highly stratified during December–January. Observational results from a seafloor acoustic doppler current profiler verify that the current is mainly dominated by a barotropic current. The monthly average sea-level-anomaly (SLA) and barotropic current vector maps confirm a cyclonic circulation in the northern GoT during November–January. The BSWA1 is located near the center of the cyclonic circulation. The BSWA1 and cyclonic circulation simultaneously enter their weakening phases, which suggests that the cyclonic circulation convergence plays a key role in maintaining the BSWA1. The BSWA2 occurs as a narrow strip concentrated along the eastern slope of the basin in the southern GoT during December–January. The southern GoT also has higher SLA and forms a congregation area of diluted water with S < 31.0 psu that enters from the north and south of this region during December–January.

Impact of Thermohaline Conditions on Vertical Variability of Optical Properties in the Gulf of Finland (Baltic Sea): Implications for Water Quality Remote Sensing

Vertical variability of inherent optical properties (IOPs) affect the water quality retrievals from remote sensing data. Here, we studied the vertical variability of IOPs and simulated apparent optical properties (AOPs) in the Gulf of Finland (Baltic Sea) under three characteristic (non)stratification conditions. In the case of mixed water column, the vertical variability of optically significant constituents (OSC) and IOPs was relatively small. While in case of stratified water column the IOPs of surface layer were three times higher compared to the IOPs below the thermocline and the IOPs were strongly correlated with the physical parameters (temperature, salinity). Measurements of IOPs in stratified water column showed that the ratio of scattering (b(440)) to absorption (a(440)) changed under the thermocline (b(440)/a(440) &amp;lt; 1) i.e., absorption became the dominant component of attenuation under thermocline while the opposite is true for the upper layer. Simulated (from IOPs) spectral irradiance reflectance (R(λ)) and spectral diffuse attenuation coefficient (Kd(λ)) from deeper layers (below thermocline) have significantly smaller magnitude and smoother shape. This becomes relevant during upwelling events—a common process in the coastal Baltic Sea. We quantified the effect of upwelling on surface water properties using simulated AOPs. The simulated AOPs (from IOPs measurements) showed a decrease of the signal up to 68.8% and an increase of optical depth (z90(λ)) from 2.3 to 4.3 m in the green part of the spectrum in case upwelled water mass reaches the surface. In the coastal waters a vertical decrease of Kd(λ) in the PAR region (400–700 nm) by 6.8% (surface to 20 m depth) was observed, while vertical decrease of chlorophyll-a (Chl-a) and total suspended matter (TSM) was 31.7 and 42.1%, respectively. The ratio R(490)/R(560)≥0.77 indicates also the upwelled water mass. The study showed that upwelling is a process that, in addition to biological activity, horizontal transport of OSC, and temperature changes, alters the optical signal of surface water measured by a remote sensor. Knowledge about the vertical variability of IOPs and AOPs relation to upwelling can help the parametrisation of remote sensing algorithms for retrieving water quality estimates in the coastal regions.

Effects of temperature and salinity on the development and survival of the embryos and zoeae I from the southern surf crab Ovalipes trimaculatus (Brachyura: Portunidae).

Ovalipes trimaculatus is a highly valued fisheries resource with high potential for aquaculture production. Still, there is need for experimental information to sustain efficient husbandry practices. In this work we analyze the combined effects of different thermo-haline conditions on the length of development and survival of embryos (6, 10, 13, 15, 18, 22, 24 ⁰C x 30, 33 ‰; 13 ⁰C x 26, 30, 33, 37 ‰) and zoeae I (13, 18, 22 ⁰C x 30, 33 ‰; 13 ⁰C x 26, 30, 33, 37 ‰) from individuals sampled in the Atlantic coast of Patagonian. Among the most relevant results, it was found that the mean length of embryogenesis decreased from 63 to 19 days with increasing temperatures, but was not affected by seawater salinity. Mean embryonic survival was significantly lower at the combination of the highest temperature and salinity tested. Also, it differed between salinity conditions. Both at 30 and 33‰, the length of the Zoea I stage significantly varied between thermal treatments, being significantly longer at 13⁰C. No zoeae I reared at 13 ⁰C survived at 37‰ and mean survival at 26‰ halved that of 30-33‰. Results obtained reduce aquaculture production costs.

Comparison of Thermohaline Optima for Juveniles of Two Sympatric Paralichthyid Flounders: Ecophysiological Evaluation of Estuarine Nursery Quality

Juvenile summer flounder Paralichthys dentatus and southern flounder Paralichthys lethostigma exhibit ontogenetic segregation during spring and summer in southeastern USA estuaries, with summer flounder remaining primarily in polyhaline regions and southern flounder migrating to oligohaline habitat. To determine physicochemical conditions contributing to optimal nursery ground function for each species, growth rates, feeding rates, and gross growth efficiencies were examined in common-garden experiments at spring and summer thermohaline regimes. Experiments were conducted on young-of-the-year (45–100 mm total length; 0.9–8.9 g) summer flounder (15–25 °C, 10–30‰) and southern flounder (15–30 °C, 0–30‰) from North Carolina, and juvenile summer flounder from Delaware (15–25 °C, 30‰ only). Over the 15–25 °C and 10–30‰ conditions common to both species, means of all dependent variables were greater in summer flounder than southern flounder. Summer flounder grew best at 21–23 °C and 21–28‰. Low salinity (0–10‰) was physiologically suboptimal, especially at high (25 °C) summer temperatures. There was a significant direct effect of location (North Carolina vs Delaware) on growth efficiency of juvenile summer flounder, but not on growth rate, feeding rate, or linear growth rate. Growth potential of southern flounder was maximum at 25–26 °C and 10–30‰, and growth efficiency was highest at mesohaline salinities; yet growth was maintained at moderate levels over a broad range of oligohaline conditions, including ≤ 10‰, even at 30 °C. Differences in thermohaline conditions that affect growth potential illustrate spatiotemporal patterns and dynamics of optimal nursery potential for these two paralichthyid flounders.

Unusually low euphausiid biomass during the warm years of 2014–2016 in the transition zone of the California Current

Euphausiids represent a significant part of the total zooplankton biomass and are a key link in the trophic web of the California Current System (CCS). During 2014–2016, the northeast Pacific experienced warming caused by two successive events, the Blob and the 2015–2016 El Niño, which affected the whole ecosystem. Here we present evidence for a strong impact of the 2014–2016 warm events on euphausiids in the Baja California region, namely two species (Euphausia pacifica and Nematoscelis difficilis) that are dominant in the CCS transition zone. Both species decreased approximately 95% in relation to the previous years (1999–2010). A similar decrease was observed for E. pacifica during the 1997–1998 El Niño, but the decrease in N. difficilis was higher in 2014–2016 and unprecedented during the 1997–2016 period. Biomass of the coastal species Nyctiphanes simplex showed negative anomalies during the Blob but not during the 2015–2016 El Niño. The tropical species Euphausia eximia and Euphausia recurva increased in biomass during the Blob in 2014 relative to the previous years, and even more during the 2015–2016 El Niño. The strong increase of E. eximia, E. recurva, and N. simplex during El Niño may have been due to upwelling activity in winter 2015–2016. Canonical correspondence analysis (CCA) was performed to assess the relation between the euphausiid community and environmental variables. The most influential variables were temperature and chlorophyll, and to a lesser extent salinity. The subarctic E. pacifica showed covariance with chlorophyll while a set of tropical species did with thermohaline conditions. However, the variance accounted for was low (20% taking the first three axis). N. difficilis did not show significant scores in the CCA suggesting that other variables such as availability of prey could be important for this carnivore species.

Benthic deep-sea fungi in submarine canyons of the Mediterranean Sea

Fungi are ubiquitous components of microbial assemblages in aquatic ecosystems, but their quantitative relevance, ecological role and diversity in benthic deep-sea ecosystems are still largely unknown. Here, we investigated patterns and drivers of benthic fungal abundance, biomass and diversity from 200 to 1000 m depth in three submarine canyons of the Mediterranean Sea (Tricase, Crotone and Squillace canyons). The Crotone and Squillace canyons, which are close to the coast and influenced by river inputs, showed significantly higher fungal abundance, biomass and diversity (as operational taxonomic units, OTUs) compared with the Tricase canyon that was far from the coast and without nearby estuaries. Fungal biomass, abundance and diversity increased with increasing concentrations of carbohydrates, which in deep-sea sediments include highly refractory organic compounds. Overall, a total of 1742 fungal OTUs, belonging to all fungal phyla known to date, were found and Ascomycota represented the dominant phylum. However, only 36% of the reads belonged to known genera. In particular, Tricase and Crotone canyons hosted the highest proportion of unknown fungal taxa, suggesting that deep-sea sediments can harbour a high number of novel fungal lineages. Our findings also reveal that fungal assemblage composition in the investigated canyons was influenced by trophic and thermohaline conditions, which may promote a high turnover diversity of benthic deep-sea fungal assemblages. Overall results reported here indicate that the submarine canyons of the Mediterranean Sea can represent hot-spots of abundant and highly diversified fungal assemblages and pave the way for a better understanding of the ecological role of fungi in the largest ecosystem on Earth.

Multilayer approach for characterization of bacterial diversity in a marginal sea: From surface to seabed

Bacteria are the most important microorganisms in the world oceans, accounting for up to 75% of the total biomass. They are responsible for fundamental biogeochemical processes and therefore often used as ecological indicators. In this study, bacteria were quantified by flow cytometry and their diversity assessed by High Throughput Sequencing (HTS) in the southern Adriatic Sea. The most abundant bacterial groups were also quantified by qPCR. The samples were collected from the surface to the seabed over a total of 16 different depths at four stations during the late winter BIOTA (BIO-Tracing Adriatic water masses) cruise conducted in March 2016. The investigated area showed unusual water mass properties and was characterized by a shallow mixed layer, which differed from the usual winter convection conditions, typical of middle-altitude ecosystems and important for the seasonal picoplankton dynamics of this area. Heterotrophic bacteria were separated into HNA (relative High Nucleic Acid content) and LNA (Low Nucleic Acid content) subpopulations with abundances up to 1.8 × 105 and 8.8 × 105 cells mL−1, respectively. HNA dominated at offshore stations reaching their maximum at depths below the euphotic zone. The bacterial community was dominated by Alphaproteobacteria, accounting for >40% of the total sequence reads and were mainly represented by the SAR11 clade (90.84%), followed by Marinimicrobia (18% of the total sequence reads), mainly represented by clade SAR406 (8.44%). Distinctive bacterial groups were found in the euphotic layer (Bacteroidetes and Actinobacteria) and aphotic layer samples (Deltaproteobacteria, Marinimicrobia, Chloroflexi, Acidobacteria and Planctomycetes). Results of the qPCR analyses further confirmed HTS results with highest abundances obtained for Alphaproteobacteria, followed by Gammaproteobacteria and Bacteroidetes. The adopted multiple approach, combining different molecular tools, critically supported by optics and flow cytometry, reveal changes in the bacterial assemblages during the unusual thermohaline conditions observed in 2016 in the southern Adriatic Sea.

Effects of Gravity Waves on Turbulence and Processes that Contribute to Mixing at a Submarine Groundwater Discharge

ABSTRACT Gallegos, G.; Marino-Tapia, I., and Valle-Levinson, A., 2016. Effects of gravity waves on turbulence and processes that contribute to mixing at a submarine groundwater discharge. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 856–860. Coconut Creek (Florida), ISSN 0749-0208. Submarine ground water discharges (SGD) around the coasts of the Yucatan Peninsula are very common due to the karstic origin of the rocks, and the abundant rain. These discharges of brackish water into the coastal sea are strong enough to alter the thermohaline conditions, they can be preferential routes for salt intrusion, and also represent an important input of nutrients and pollutants. The mixing on these SGDs is a spontaneous and turbulent process, and its study is important for the understanding of dispersion of materials in regions influenced by these features...

Distribution and salinity tolerance of marine mysids from a subtropical estuary, Brazil

ABSTRACTWe studied the spatial and temporal distribution pattern of three marine mysids (Chlamydopleon dissimile, Metamysidopsis elongata atlantica and Mysidopsis coelhoi) from the Cananeia-Iguape Coastal System, southeast Brazil, in relation to environmental variables and zooplankton abundance. We also analysed mysid reproductive traits, and tested their tolerance to salinity gradients in laboratory experiments. Salinity was identified as a major factor influencing mysid spatial and temporal distribution, selectively limiting their distribution within the estuary. Chlamydopleon dissimile and M. coelhoi were common, but occurred at low abundances throughout the year, whereas the numerically dominant M. elongata atlantica had abundance peaks in spring, when thermohaline conditions were more favourable. Mysid brood size varied interspecifically; the occurrence of juveniles throughout the year indicated that mysids breed continuously in the region. The high biomass of M. elongata atlantica observed in spring confirms the importance of mysids in coastal regions' food webs.

CARACTERÍSTICAS OCEANOGRÁFICAS EN LA ISLA MALPELO Y SU RELACIÓN CON LA CUENCA OCEÁNICA DEL PACÍFICO COLOMBIANO

Malpelo Island forms the insular ecoregion of the Colombian Pacific, and is composed by a mosaic of terrestrial ecosystems, and unique coastal and shallow subtidal systems. Considering its insular nature, the oceanographic features of this locality are expected to be related with the physical and chemical dynamics of the Eastern Tropical Pacific (ETP) and be modulated by the regional dynamic of the Colombian Pacific Oceanic Basin (COPC in Spanish). In this work, in situ data was used to describe the thermohaline conditions in the water column in Malpelo Island and identify key water mass during the two contrasting hydro-meteorological periods of the COPC. Furthermore, we analyzed the thermal and haline variability in the COPC and defined the surface geostrophic flow from in situ oceanographic data during the same time in order to evaluate its effect on the oceanographic conditions in the pelagic environment off Malpelo Island.

Assessment of the Black Sea observing system. A focus on 2005-2012 Argo campaigns

An observing system in the Black Sea combining remote sensing data such as sea level anomalies from altimetry, sea surface temperature from satellite radiometer and data from Argo floats has been analyzed with the aim to quantify the contribution of different information sources when reconstructing the ocean state. The main research questions are: (1) do Argo float measurements substantially impact the quality of estimates, (2) what is the dependence of this quality upon the data and sampling used, and (3) are there specific Black Sea issues? Numerical model output and statistical analysis were used for this purpose. It has been demonstrated that the statistical method performs in a consistent way reproducing known geophysical patterns. Maximum footprints of sea level, salinity and temperature were illustrated, most of them clearly connected with specific thermohaline conditions and the general circulation. Reduced analysis capabilities were identified as associated with a low level of dynamical coupling between the shelf and the open ocean, mesoscale dynamics and representation of diapycnic processes in the models. The accuracy of Argo pressure measurements appeared very important to resolve the extremely sharp stratification in the upper layers. The present-day number of Argo floats operating in the Black Sea of about 10, seems optimal for operational purposes.

Structure and variability of the boundary current in the Eurasian Basin of the Arctic Ocean

The Arctic Circumpolar Boundary Current (ACBC) transports a vast amount of mass and heat around cyclonic gyres of the deep basins, acting as a narrow, topographically-controlled flow, confined to the continental margins. Current observations during 2002–2011 at seven moorings along the major Atlantic Water (AW) pathway, complemented by an extensive collection of measured temperatures and salinities as well as results of state-of-the-art numerical modeling, have been used to examine the spatial structure and temporal variability of the ACBC within the Eurasian Basin (EB). These observations and modeling results suggest a gradual, six-fold decrease of boundary current speed (from 24 to 4cm/s) on the route between Fram Strait and the Lomonosov Ridge, accompanied by a transformation of the vertical flow structure from mainly barotropic in Fram Strait to baroclinic between the area north of Spitsbergen and the central Laptev Sea continental slope. The relative role of density-driven currents in maintaining AW circulation increases with the progression of the ACBC eastward from Fram Strait, so that baroclinic ACBC forcing dominates over the barotropic in the eastern EB. Mooring records have revealed that waters within the AW and the cold halocline layers circulate in roughly the same direction in the eastern EB. The seasonal signal, meanwhile, is the most powerful mode of variability in the EB, contributing up to ~70% of the total variability in currents (resolved by moorings records) within the eastern EB. Seasonal signal amplitudes for current speed and AW temperature both decrease with the eastward progression of AW flow from source regions, and demonstrate strong interannual modulation. In the 2000s, the state of the EB (e.g., circulation pattern, thermohaline conditions, and freshwater balance) experienced remarkable changes. Results showing anomalous circulation patterns for an extended period of 30 months in 2008–2010 for the eastern EB, and a two-core AW temperature structure that emerged in this region of the Arctic Ocean in the most recent decade, suggest a shift of the EB toward a new, more dynamic state. This also likely suggests that the EB interior will become more susceptible to future climate change. Evaluating properties of the ACBC, its temporal variability at time scales from a season to several years, and possible governing mechanisms, this study contributes to a better understanding of Arctic Ocean circulation.

Late Quaternary variations of the southern westerly wind belt and its influences on aquatic ecosystems and glacier extend within the southernmost Andes

The southern tip of South America is year-round influenced by the southern westerly wind belt (SWW) causing extremely high precipitation along the Chilean coast and the Andes south of 33°S with maximum values of 3000 to >10 000 mm/year within the SWW core between 49 to 55°S which is unique for temperate regions on the global scale. Due to this key position within the global atmospheric and oceanic framework we have investigated a large number of Late Quaternary climate archives during the last decade including fjord and lake sediments, peats, stalagmites and tree rings. To improve our proxy understanding in these various archives, climate as well as hydrological monitoring stations were operated since 1999. Here we present one-year monitoring data, which document the short term variability of climate and thermohaline conditions and related fertility in the fjord surface water. In this context we also analysed the interplay between palaeo-precipitation and related freshening of surface water (low nitrate and phosphate) and the terrestrial nutrient supply to the fjords during the last 5 ka BP using new salinity and productivity proxies of a fjord sediment core. Lake sediment cores and a stalagmite record document high chemical denudation rates, and metal leaching occurs on a weakly buffered granitoid basement and areas covered by acidic peaty soils. The partly climate-controlled changes in the iron and trace metal mobility have profound implications for both terrestrial and aquatic ecosystems. Based on the investigated archives we also reviewed SWW changes and regional temperature variations during the past 30 ka BP and their implication for Glacial and Holocene glacier advances.

Conditions of the formation and runoff of shelf waters in different water areas of the Arctic and Antarctic

The comparative analysis of hydrometeorological and topographic conditions of the formation and runoff of dense shelf waters on the shelves and continental slopes in different water areas of the Arctic and Antarctic demonstrates that they are similar in many aspects but there are some differences as well. In the Antarctic, these conditions are more favorable. The thermohaline conditions of the formation and runoff of shelf waters in the Arctic and Antarctic are also similar. The similarity of different conditions enables to construct the adaptive physical model of the shelf and slope cascading of shelf waters generalized for different polar water areas. It is based on the analysis of historical and present-day in situ data in the areas of margins of shelves and slopes in the Arctic and Antarctic, observations in the areas of flaw polynyas, and passing ice and meteorological observations, as well as on taking account of some general results of laboratory and theoretical investigations of the dense liquid runoff along the inclined bottom.

Variability of water mass properties in the last two decades in the South Adriatic Sea with emphasis on the period 2006–2009

Spatially averaged temperature and salinity profiles from individual cruises between 1990 and 2009 were analysed to outline the temporal evolution of water mass properties in the deep convection site in the South Adriatic Pit (SAP). The long-term variability in thermohaline conditions has been explained and related to a close feedback mechanism between the Ionian and the Adriatic Sea. Prominent influences of the Eastern Mediterranean Transient are manifested in changes in the vertical temperature and salinity patterns in the South Adriatic, and the whole studied period was divided into three stages according to the main thermohaline characteristics: 1990–1995, 1995–2004 and the last period from 2005 onwards. Particular attention was given to data collected during 2006–2009, which permitted us to situate the actual thermohaline properties in the context of the decadal variability. This last period was characterised by a very low production of dense water in the northern basin during 2007, while from winter 2008 high production of North Adriatic Deep Water (NAdDW) and Adriatic Deep Water (AdDW) in the northern and southern basins, respectively, was observed. Finally, we used the Optimum Multiparameter Analysis (OMP) to identify the percentages of the different water masses contained in the SAP, and this highlighted some differences between two recent periods studied (2007 and 2008) and the production of dense waters.

Temporal variability of the physical and chemical water characteristics at a coastal monitoring observatory: Station ENSENADA

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 Niña 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 (<50 km) off Ensenada in the northern BC region. Consequently, station ENSENADA would be a good location to high-frequency monitors the oceanographic conditions of the transitional region between tropical/subtropical and subarctic systems of the California Current System.

A box model of circulation and melting in ice shelf caverns

A simple box model of the circulation into and inside the ocean cavern beneath an ice shelf is used to estimate the melt rates of Antarctic glaciers and ice shelves. The model uses simplified cavern geometries and includes a coarse parameterization of the overturning circulation and vertical mixing. The melting/freezing physics at the ice shelf/ocean interface are those usually implemented in high-resolution circulation models of ice shelf caverns. The model is driven by the thermohaline inflow conditions and coupling to the heat and freshwater exchanges at the sea surface in front of the cavern. We tune the model for Pine Island Glacier and then apply it to six other major caverns. The dependence of the melting rate on thermohaline conditions at the ice shelf front is investigated for this set of caverns, including sensitivity studies, alternative parameterizations, and warming scenarios. An analytical relation between the melting rate and the inflow temperature is derived for a particular model version, showing a quadratic dependence of basal melting on small values of the temperature of the inflow, which changes to a linear dependence for larger values. The model predicts melting at all ice shelf bases in agreement with observations, ranging from below a meter per year for Ronne Ice Shelf to about 25 m/year for the Pine Island Glacier. In a warming scenario with a one-degree increase of the inflow temperature, the latter glacier responds with a 1.4-fold increase of the melting rate. Other caverns respond by more than a tenfold increase, as, e.g., Ronne Ice Shelf. The model is suitable for use as a simple fast module izn coarse large-scale ocean models.