Distinct Water Masses Research Articles

Foraging distributions of little auks Alle alle across the Greenland Sea: implications of present and future Arctic climate change

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 415:283-293 (2010) - DOI: https://doi.org/10.3354/meps08749 Foraging distributions of little auks Alle alle across the Greenland Sea: implications of present and future Arctic climate change Nina Karnovsky1,*, Ann Harding2, Wojciech Walkusz3, Sławomir Kwaśniewski3, Ilona Goszczko3, Josef Wiktor Jr3, Heli Routti4, Allison Bailey1, Laurel McFadden1, Zachary Brown1, Grégory Beaugrand5, David Grémillet6,7 1Department of Biology, Pomona College, 175 W 6th St., Claremont, California 91711, USA 2Environmental Science Department, Alaska Pacific University, 4101 University Drive, Anchorage, Alaska 99508, USA 3Institute of Oceanology, Polish Academy of Sciences, Powstańców Warszawy 55, 81-712 Sopot, Poland 4Norwegian Polar Institute, Polar Environmental Centre, 9296 Tromsø, Norway 5Centre National de la Recherche Scientifique, Laboratoire d’Océanologie et de Géosciences, UMR CNRS 8187 LOG, Université des Sciences et Technologies de Lille 1, Station Marine, 28 avenue Foch, 69360 Wimereux, France 6Centre National de la Recherche Scientifique, CEFE, 1919 route de Mende, F 34293 Montpellier, Cedex 5, France 7Percy FitzPatrick Institute, DST/NRF Centre of Excellence, University of Cape Town, Rondebosch 7701, South Africa *Email: nina.karnovsky@pomona.edu ABSTRACT: The Arctic is undergoing widespread warming. In order to understand the impact of climate change on Arctic marine food webs, we studied the at-sea distribution of foraging little auks in contrasting conditions of the Greenland Sea. While the eastern side of the Greenland Sea has experienced recent warming, the western side is still dominated by cold, Arctic water in the East Greenland Current. We hypothesized that foraging little auks would be found in greatest abundance in cold Arctic waters bearing more lipid-rich prey, allowing them to deliver more energy-rich food to their chicks. To test our hypotheses, we made ship-borne bird observations and zooplankton tows, as well as analyses of chick meals at 2 little auk colonies adjacent to 3 distinct water masses in the Greenland Sea. Associated with the coldest water in the East Greenland Current, we found the highest concentrations of large Calanus copepods (C. glacialis and C. hyperboreus), as well as the highest concentrations of foraging little auks, indicating a relationship that is likely to be disrupted by increasing water temperatures. To assess potential future impacts of ocean warming, we used a coupled atmosphere–ocean global climate model (AOGCM) to predict Greenland Sea sea-surface temperatures over the study area at the end of the 21st century. Our results suggest that 4 of 8 little auk breeding colonies in the North Atlantic may be negatively impacted as temperatures exceed the thermal preferenda of large Calanus, which is the preferred prey of little auks during the breeding season. KEY WORDS: At-sea observations · Calanus copepod · Climate model · East Greenland Current · Seabird · Little auk · Sea temperature · West Spitsbergen Current Full text in pdf format PreviousNextCite this article as: Karnovsky N, Harding A, Walkusz W, Kwaśniewski S and others (2010) Foraging distributions of little auks Alle alle across the Greenland Sea: implications of present and future Arctic climate change. Mar Ecol Prog Ser 415:283-293. https://doi.org/10.3354/meps08749Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 415. Online publication date: September 29, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

The COPAS’08 expedition to the Patagonian Shelf: Physical and environmental conditions during the 2008 coccolithophore bloom

Here we present observations of the hydrography of the Patagonian Shelf, shelf break and offshore waters, with reference to the environmental conditions present during the period of peak coccolithophore abundance. Analysis of a hydrographic dataset collected in December 2008 (austral spring/summer), as part of the Coccolithophores of the Patagonian Shelf (COPAS) research cruise, identified 5 distinct surface water masses in the region between 37°S and 55°S. These water masses, identified through salinity gradients, displayed varying mixed layer depths, macronutrient inventories and chlorophyll- a fluorescence. Subantarctic Shelf Water (SSW), located to the north of the Falkland Islands and extending north along the shelf break, was also host to a large coccolithophore bloom. The similarities between the distribution of calcite, as seen in remote sensing data, and SSW indicate that the coccolithophore bloom encountered conditions conducive to bloom development within this water mass. Analysis of chemical and environmental data also collected during the COPAS cruise revealed that many of the commonly cited conditions for coccolithophore bloom development were present within SSW (e.g. low N:P ratio, high N:Si ratio, shallow mixed layer depth). In the other water masses present on the Patagonian Shelf greater variability in these same parameters may explain the more diffuse concentration of calcite, and the smaller size of possible coccolithophore blooms. The distribution of SSW is strongly influenced by the latitudinal variation in shelf break frontal width, which varies from 20 to 200 km, and consequently strong hydrographic controls underlie the position of the coccolithophore bloom during austral summer.

Otolith elemental signatures reflect residency in coastal water masses

We examined variability in otolith chemistry of wild caught fish in relation to in situ temperature and salinity within the California Current System. Barium, magnesium, and iron from the most recent growth zone in otoliths differentiated pelagic juvenile shortbelly rockfish (Sebastes jordani) residing in water masses with distinct temperature and salinity properties from central and southern California spanning nearly 500 km of coastline. The 3-element signature also discriminated fish that resided in different water masses that were associated with mesoscale cyclonic eddy circulation in the Santa Barbara Channel. Variability in otolith chemistry reflected the spatial patterns of both horizontal gradients and vertical gradients in water mass properties related to circulation. Although we found that the concentrations of particular elements in otoliths were correlated to ambient temperature or salinity, we suggest that these parameters are more useful as an identifying signature of distinct water masses associated with unique otolith signatures rather than as factors directly affecting otolith chemistry. Other factors varying among the water masses or among the fish populations residing in the water masses may also affect otolith chemistry. We discuss how oceanographic phenomena associated with the 1997–1998 El Nino and the persistent, recirculating eddy in the Channel may have affected coastal ocean conditions and variation in otolith chemistry of fish in the study area.

Climatic regulation of Clinocardium ciliatum (bivalvia) growth in the northwestern Barents Sea

We examined the growth of the Arctic bivalve Clinocardium ciliatum in the Barents Sea to evaluate the effect of oceanographically distinct water masses on growth and to assess the influence of climatic forcing on ecological processes over decadal scales. Analysis of annually-deposited growth lines in shells of 22 individuals from 3 stations allowed us to assess growth conditions from 1977–2006, encompassing both warmer and colder climatic phases of the 20th century. Growth rates of juvenile specimens (6–13 years) were highest in Atlantic water, resulting in a 20% greater average shell size compared to similarly aged individuals from Arctic water or at the Polar Front. This may reflect comparatively warmer sea temperatures and/or greater food supplies in regions of the Barents Sea dominated by Atlantic water. Despite different absolute growth rates, temporal patterns of ontogenetically-adjusted incremental growth (i.e. Standard Growth Index = SGI) were similar at all sites, with low but increasing SGI throughout the 1980s and peaking in 1994 or 1995. An abrupt decline starting in 1996 led to low SGI values for most years from the turn of the century to the last year of bivalve growth in 2006. The decline in SGI coincides with abrupt phase shifts in two hemispheric oscillatory indices: the North Atlantic Oscillation (NAO) and the Arctic Climate Regime Index (ACRI). The strongest statistical relationships were found between standardized growth and the ACRI and its local manifestations through precipitation and sea ice cover. The ACRI explained 51% of the variation in growth from all the samples, while ACRI, annual precipitation, and ice-free days together explained 65% of the growth variability. Using a two-year running mean of the ACRI improved these relationships substantially and indicates a possible lag in the relationship between external forcing and bivalve growth. These results show that benthic communities in this area are intricately linked to regional climatic forcing and that the predicted increase in Atlantic water influence in the Barents Sea in response to climate change will impact growth of benthic organisms.

A mesoscale eddy driving spatial and temporal heterogeneity in the productivity of the euphotic zone of the northeast Atlantic

In this paper we show how different water masses from a similar geographic region provide an explanation for perturbations in the signal of declining productivity at the Porcupine Abyssal Plain (PAP) study site in the Northeast Atlantic. Furthermore we show that the passage of these different water masses is affected by the filamentary instabilities of a cyclonic eddy just southwest of the PAP site. We describe a high-resolution spatial hydrographic survey conducted with a towed instrument package, complemented by biogeochemical sampling. Maximum rates of primary production of 110 mmol C m-2 d-1 seen at the centre of the survey area were associated with the passage of an eddy filament and were enhanced 3 fold relative to far-field conditions (∼36 mmol C m-2 d-1). The rotation and stirring influence of the eddy resulted in the sequential passage of 3 distinct water masses past the observation point. This understanding of the lateral stirring around the site enabled us to explain the sharp changes observed in daily primary production rates and other biogeochemical parameters. The spatial survey also revealed a fluorescence maxima associated with the cyclonic eddy that was laterally displaced northwards away from the core, an observation supportive of recent modelling studies.

The circulation pattern in the Mediterranean Sea: issues for modeller consideration

The Mediterranean Sea is one of the most thoroughly studied water bodies in the world Its location and geopolitical importance since before the rise of the Roman Empire has stimulated study since the early eras of human civilisation. More recently, the Sea, like many of the world’s oceans, has attracted the attention of engineers considering the extraction of renewable energy.This paper outlines the complexity of the domains which underpinning modelling must consider.The Mediterranean Sea is a semi-closed water body connected to the Atlantic Ocean through the Strait of Gibraltar in its far western extremity.The main basin is divided into two principal sub-basins, which together cover a surface area of 2.5 × 106 km2, with a maximum measured depth of 5.1km. The Sea is characterised by its three distinct water masses: surface, intermediate and deep.These cover the whole Mediterranean basin and circulate independently.The general circulation pattern of the Sea has its own features and characteristics, which are described in this paper, drawing upon published research results.

Understanding Oceanic Migrations with Intrinsic Biogeochemical Markers

Migratory marine vertebrates move annually across remote oceanic water masses crossing international borders. Many anthropogenic threats such as overfishing, bycatch, pollution or global warming put millions of marine migrants at risk especially during their long-distance movements. Therefore, precise knowledge about these migratory movements to understand where and when these animals are more exposed to human impacts is vital for addressing marine conservation issues. Because electronic tracking devices suffer from several constraints, mainly logistical and financial, there is emerging interest in finding appropriate intrinsic markers, such as the chemical composition of inert tissues, to study long-distance migrations and identify wintering sites. Here, using tracked pelagic seabirds and some of their own feathers which were known to be grown at different places and times within the annual cycle, we proved the value of biogeochemical analyses of inert tissue as tracers of marine movements and habitat use. Analyses of feathers grown in summer showed that both stable isotope signatures and element concentrations can signal the origin of breeding birds feeding in distinct water masses. However, only stable isotopes signalled water masses used during winter because elements mainly accumulated during the long breeding period are incorporated into feathers grown in both summer and winter. Our findings shed new light on the simple and effective assignment of marine organisms to distinct oceanic areas, providing new opportunities to study unknown migration patterns of secretive species, including in relation to human-induced mortality on specific populations in the marine environment.

The effects of temperature and water concentration on the otolith incorporation of barium and manganese in black rockfish Sebastes melanops

Observations of multiple years of geographic variation in [Ba:Ca](otolith) and [Mn:Ca](otolith) in black rockfish Sebastes melanops prompted this study to examine the effects of temperature and water concentration on the otolith incorporation of Ba and Mn in this wholly marine species. The replicated experiment design consisted of two water temperatures (7.4 and 13.0 degrees C) and four water concentrations of Ba:Ca and Mn:Ca. A positive, linear relationship between [Ba:Ca](water) and [Ba:Ca](otolith) was observed at both temperatures. A positive temperature effect was also observed with mean partition coefficients for Ba (D(Ba)) greater in the 13 degrees C than in the 7.4 degrees C treatments (mean = 0.061 and 0.048, respectively). There was no relationship between [Mn:Ca](water) and [Mn:Ca](otolith) although a negative temperature effect was observed. Mean partition coefficients for Mn (D(Mn)) were lower in the 13 degrees C than in the 7.4 degrees C treatments (mean = 0.027 and 0.036, respectively). The data presented support the assumption of a positive, linear relationship between water and otolith Metal:Ca concentrations for Ba:Ca but not for Mn:Ca. Thus, although indicative of residence in distinct water masses, observed variation in [Metal:Ca](otolith) may not reflect variation in water concentration and can be affected by temperature. Caution should be applied in the interpretation of geographic variation of [Mn:Ca](otolith) until the mechanisms regulating its incorporation are more fully understood.

Transequatorial Migrations by Basking Sharks in the Western Atlantic Ocean

The world's second largest fish, the basking shark (Cetorhinus maximus), is broadly distributed in boreal to warm temperate latitudes of the Atlantic and Pacific oceans from shallow coastal waters to the open ocean. Previous satellite archival tagging in the North Atlantic has shown that basking sharks move seasonally, are often associated with productive frontal zones, and may make occasional dives to mesopelagic depths. However, basking sharks are thought to be restricted to temperate latitudes, and the extent to which they exploit deeper-water habitat remains enigmatic. Via satellite archival tags and a novel geolocation technique, we demonstrate here that basking sharks are seasonal migrants to mesopelagic tropical waters. Tagged sharks moved from temperate feeding areas off the coast of southern New England to the Bahamas, the Caribbean Sea, and onward to the coast of South America and into the Southern Hemisphere. When in these areas, basking sharks descended to mesopelagic depths and in some cases remained there for weeks to months at a time. Our results demonstrate that tropical waters are not a barrier to migratory connectivity for basking shark populations and highlight the need for global conservation efforts throughout the species range.

A conceptual model of the strongly tidal Columbia River plume

The Columbia River plume is typical of large-scale, high discharge, mid-latitude plumes. In the absence of strong upwelling winds, freshwater from the river executes a rightward turn and forms an anticyclonic bulge before moving north along the Washington coast. In addition to the above dynamics, however, the river plume outflow is subject to large tides, which modify the structure of the plume in the region near the river mouth. Observations based on data acquired during a summer 2005 cruise indicate that the plume consists of four distinct water masses; source water at the lift-off point, and the tidal, re-circulating and far-field plumes. In contrast to most plume models that describe the discharge of low-salinity estuary water into ambient high-salinity coastal water, we describe the Columbia plume as the superposition of these four plume types. We focus primarily on a conceptual summary of the dynamics and mutual interaction of the tidal and re-circulating plumes. The new tidal plume flows over top of the re-circulating plume and is typically bounded by strong fronts. Soon after the end of ebb tide, it covers roughly 50–100% of the re-circulating plume surface area. The fronts may penetrate well below the re-circulating plume water and eventually spawn internal waves that mix the re-circulating plume further. The re-circulating plume persists throughout the tidal cycle and corresponds to a freshwater volume equivalent to 3–4 days of river discharge. Finally, the plume water masses are distinguished from one another in term of surface chlorophyll concentration, suggesting that the above classification may also describe different biological growth regimes. The low-salinity re-circulating plume serves as an extension of the estuary into the coastal ocean, or an “estuary at sea”, because residence times during periods of high river flow are greater than those in the estuary.

Effects of macrophytes and terrestrial inputs on fluorescent dissolved organic matter in a large river system

We studied the contribution of aquatic macrophytes and allochthonous sources to the pool of fluorescent dissolved organic matter (FDOM) in a large river system composed of several distinct water masses that flow alongside one another in the same riverbed. Using three dimensional fluorescence combined with parallel factor analysis (PARAFAC), we characterized FDOM found in the St. Lawrence River (Lake Saint-Pierre, Quebec, Canada), and from macrophyte leaching experiments. Eight fluorescent components were identified, three of which were dominant in macrophyte experiments and were similar to protein-like, autochthonous fluorophores identified in previous studies. The remaining components corresponded to humic and fulvic acids, and a principal component analysis revealed that their distribution in Lake Saint-Pierre was different than that of protein-like fluorophores, suggesting a different origin. Concentrations of dissolved organic carbon were strongly associated with the distribution of the allochthonous components. The distribution of protein-like FDOM in Lake Saint-Pierre matched that of macrophytes in the lake and the abundance of allochthonous FDOM was explained by the connectivity with the terrestrial ecosystem. Nearshore water masses carrying large loads of newly imported organic matter from proximal tributaries showed the maximum abundances and the older water masses, from the center of the lake, carried smaller quantities of terrestrial organic matter, thus originated mainly from Lake Ontario, several hundred kilometers upstream of Lake Saint-Pierre. This study demonstrates that macrophytes are a net source of protein-like FDOM and could represent an important supply of autochthonous DOM in shallow, productive environments.

Linking isotopic and migratory patterns in a pelagic seabird

The value of stable isotope analysis in tracking animal migrations in marine environments is poorly understood, mainly due to insufficient knowledge of isotopic integration into animal tissues within distinct water masses. We investigated isotopic and moult patterns in Cory's shearwaters to assess the integration of different stable isotopes into feathers in relation to the birds' transoceanic movements. Specimens of Mediterranean Cory's shearwater Calonectris diomedea diomedea caught accidentally by Catalan longliners were collected and the signatures of stable isotopes of C (delta(13)C), N (delta(15)N) and S (delta(34)S) were analysed in 11 wing and two tail feathers from 20 birds, and in some breast feathers. Based on isotopic signatures and moult patterns, the feathers segregated into two groups (breeding and wintering), corresponding to those grown in the Mediterranean or Atlantic regions, respectively. In addition, feathers grown during winter, i.e. moulted in Atlantic waters, were grouped into two isotopically distinct profiles, presumably corresponding to the two main wintering areas previously identified for Mediterranean Cory's shearwater in tracking studies. N signatures mainly indicated the Mediterranean-to-Atlantic migration, whereas C and S signatures differed according to the Atlantic wintering area. Our results indicate that isotopic signatures from distant oceanic regions can integrate the feathers of a given bird and can indicate the region in which each feather was grown. This study thus underscores how stable isotope analysis can link marine animals to specific breeding and wintering areas, and thereby shed new light on studies involving assignment, migratory connectivity and carry-over effects in the marine environment.

Ship Observations of the Tropical Pacific Ocean along the Coast of South America

Abstract In October 2007 the NOAA ship Ronald H. Brown sailed southward within 300 km of the coast of Ecuador and Peru, sampling surface meteorology, air–sea turbulent and radiative fluxes, cloud properties, and upper-air soundings from the equator to 20°S. Two distinct water masses characterize the coastal region: cold-pool water below 19°C in the Southern Hemisphere, and warm-pool water above 20°C to the north, with a transition between the water masses at 2.5°S. Net turbulent and radiative fluxes warm the cool water south of 2.5°S by 100 W m−2 but do not warm the equatorial water significantly. Winds blow parallel to the shore, about 5 m s−1 over the cold pool and 7 m s−1 over the equator. Stratocumulus clouds are remarkably solid over the coastal cold pool, with only brief periods of partial clearing, mostly in the afternoon. Lower aerosol concentrations and thicker clouds observed farther from the coast on 22–23 October are coincident with a pocket of open cells seen to the west and southwest of the ship. Observations from this cruise and other NOAA Stratus cruises (2001 and 2003–07) are suitable for comparison with model simulations and provide context for future field experiments. These datasets are publicly available.

Surprising return of deep convection to the subpolar North Atlantic Ocean in winter 2007–2008

In the process of open-ocean convection in the subpolar North Atlantic Ocean, surface water sinks to depth as a distinct water mass, the characteristics of which affect the meridional overturning circulation and oceanic heat flux. In addition, carbon is sequestered from the atmosphere in the process. In recent years, this convection has been shallow or non-existent, which could be construed as a consequence of a warmer climate. Here we document the return of deep convection to the subpolar gyre in both the Labrador and Irminger seas in the winter of 2007–2008. We use profiling float data from the Argo programme to document deep mixing. Analysis of a variety of in situ, satellite and reanalysis data shows that contrary to expectations the transition to a convective state took place abruptly, without going through a phase of preconditioning. Changes in hemispheric air temperature, storm tracks, the flux of fresh water to the Labrador Sea and the distribution of pack ice all contributed to an enhanced flux of heat from the sea to the air, making the surface water sufficiently cold and dense to initiate deep convection. Given this complexity, we conclude that it will be difficult to predict when deep mixing may occur again.

Phytoplankton dynamics related to water mass properties in the Gulf of Gabes: Ecological implications

The spatial distribution of chlorophylls and carotenoids was recorded throughout the Gulf of Gabes (South Ionian Sea) in March 2007, and was related to patterns of the physical structure and the nutrient concentrations. Two distinct water masses were identified based on the temperature and salinity ( T– S) analysis: a cool and less salty Modified Atlantic Water (MAW) and a saltier Mediterranean Mixed Water (MMW). There was no significant difference in the mean nitrogen and phosphate concentrations between MMW and MAW, although the silica values were significantly higher in MAW. The Integrated chlorophyll a mean value was about 4 mg m − 2 , with a maximum of 13 mg m − 2 at MAW stations. Higher Chlorophyll a records in typical MAW stations were mainly due to chlorophytes, which contributed up to 58% of the pigments concentrations in the MAW and about 46% in the MMW. The contribution of chlorophytes to total Chlorophyll a was found to be relatively stable throughout the water column. The contribution of diatoms, which were twofold higher in the MMW than in the MAW, did not exceed 17% of chlorophyll a and was mainly due to subsurface maxima. The chlorophytes, pelagophytes, prymnesiophytes and cryptophytes all together accounted for more than 77% of total chlorophyll a in the MAW and about 67% in the MMW. There were statistically significant differences between MMW and MAW in the pigment contribution of cyanobacteria and pelagophytes. These two taxa accounted for 13% and 24% of chlorophyll a respectively in the MAW and MMW indicating that these differences concerned phytoplankton classes at relatively low contributions to total chlorophyll a.

Evidences of continental groundwater inputs to the shelf zone in Albardão, RS, Brazil

The southern coastal region of Brazil is highly productive and many of its oceanographic processes are still poorly understood due to a great number of forces, such as the continental input from the Plata River and Patos Lagoon, several distinct oceanic water masses, and a complex contribution from groundwater. The shelf near Albardão is highly rich in dissolved nutrients, particularly in the coastal zone. The narrow sandy barrier that separates the ocean from Mangueira Lagoon has led us to wonder about the possibility of groundwater, and if it might play a role in the productivity of the surrounding area. In order to test this hypothesis, nutrient data from Mirim and Mangueira Lagoons and from Albardão were collected during a rainy period. The present work shows the need to include groundwater transport from Mangueira Lagoon to the coastal zone as one of the main sources for the productivity in that region. However, for such phenomenon to be quantified and better understood, it becomes necessary to use natural isotopes as tracers of the underground input.

Temporal patterns of phytoplankton assemblages, size spectra and diversity during the wane of aPhaeocystis globosaspring bloom in hydrologically contrasted coastal waters

The space–time dynamic of phytoplankton diversity and succession was investigated during the wane of aPhaeocystis globosaspring bloom in four distinct hydrological sub-systems of the eastern English Channel. Nutrients, chlorophyll-a concentrations, and phytoplankton composition, standing stocks, size spectra and diversity were monitored during three key periods in 2003: late spring, early summer and summer. Two consecutive diatom assemblages were observed, respectively dominated by: (i) small colonial species (<100 μm;Melosirasp.,Diploneissp. andNavicula transitans) in April; and (ii) large fine-walled cells (>200 μm;Guinardia striataandRhizosolenia imbricata) in May and July. This shift in diatom composition appeared to be related to the potentially limitating silicic acid in early summer. Specific phytoplankton assemblages identified in distinct water masses have evolved from a mature/senescent community towards a relatively homogeneous aestival structure of dominant species that might have been triggered by the wane of theP. globosabloom. Our results also identified a strong heterogeneity in the distribution of secondary species between distinct water masses during the summer period, suggesting that the magnitude of the observed patterns was intrinsically related to the hydrological properties prevailing in each sub-system. The identification of distinct temporal patterns in phytoplankton species diversity and succession following the wane of a spring bloom at relatively small spatial scales (i.e. <10 km) is discussed in the framework ofP. globosablooms in particular and phytoplankton blooms in general and is suggested to have potentially strong consequences on food web dynamics and the carbon cycle in coastal ecosystems.

Tidal-induced inorganic carbon dynamics in the Strait of Gibraltar

This study presents the distribution of dissolved inorganic carbon (DIC) along the Strait of Gibraltar, its tidal-induced variability, as well as the inorganic carbon exchange between the Atlantic Ocean and Mediterranean Sea. During November 2003, water column samples were collected at nine stations to measure total alkalinity (TA), pH, and dissolved oxygen (DO) for the spatial characterization of the carbonate system. At the same time, anchored samplings were carried out, above the Camarinal Sill and in the Eastern Section of the Strait, in order to assess the tidal mixing effects for oxygen and DIC distribution on the water column. Three distinct water masses can be discerned in this area: the Surface Atlantic Water (SAW), the Mediterranean Water (MW), and the less abundant North Atlantic Central Water (NACW). The observations show an increase in the DIC and a decrease in oxygen concentration with depth, related to the different physico-chemical features of each water mass. The results show the high time-dependence of the vertical distribution of DIC with the interface oscillation, affected by the intense mixing processes taking place in the Strait. Intense mixing episodes over the Camarinal Sill are responsible for an increase in the DIC concentrations in the upper layer of the Eastern Section of the Strait. Higher DIC concentrations in the Mediterranean than in the Atlantic waters are responsible for a net DIC transport of 1.47×10 12 mol C yr −1 to the Atlantic Ocean. Nevertheless, the net exchange is highly sensitive to the interface definition, as well as to the estimate of water volume transport used.

Acoustic methods for water mass delineation in coastal marine ecosystems

Acoustical methods play an important role in the in the study of nutrient sources for coral reef ecosystems in the south Florida coastal ocean. Many nutrients released into the coastal ocean are released in distinct water masses such as inlet discharge plumes, wastewater outfall discharge plumes, and hurricane-induced re-suspensions. Using water column acoustic backscatter profiles, obtained via either ship-borne instrumentation or in-situ instrumentation, multidimensional images of nutrient bearing water masses are derived. Said images are of assistance in the design of chemical and biological sampling efforts. Examples of water mass imaging will be presented as well as the use of such images in the design of water quality sampling programs. Using a combination of acoustic backscatter, Doppler current profilers, nutrient (nitrate, nitrite, silica, phosphate, ammonia) samples and microbiological (fecal, protozoa, viruses) samples, flux estimates of said quantities may be made for inlet discharges. Results will be presented for a south Florida inlet having an average net seaward discharge of approximately 200 million gallons per day. Selected acoustic images of treated waste water effluent plumes will be presented and compared with plume spatial distributions inferred from conservative plume tracer studies.

Water masses and biogeography of picoeukaryote assemblages in a cold hydrographically complex system

We investigated the influence of geographic distance, environmental variables, and water mass origin on picoeukaryote (phytoplankton and other protists <3 µm) assemblages to assess the presence of biogeographic patterns. The study region was an area of converging Arctic and Atlantic currents where several distinct water masses were overlain and intersecting. Denaturing gradient gel electrophoresis (DGGE) profiles of assemblages revealed 42 distinct band types overall, with minimum richness (8 band types) in Arctic surface water and Atlantic deep water, and maximum richness (22 band types) in regions of water mass mixing. Sequencing of DGGE bands revealed that most sequences (78 of 98) matched uncultured clones from major taxonomic marine groups, including the Acantharea, Bacillariophyceae, Cercozoa, Chrysophyceae, Dinophyceae, Prasinophyceae, Prymnesiophyceae, and stramenopiles, as well as the novel marine stramenopiles (MAST), alveolate groups I and II, and picobiliphytes. Multivariate statistical analysis of DGGE profiles revealed that picoeukaryote assemblage composition was positively correlated with geographic proximity, abiotic environmental conditions (salinity, photosynthetically active radiation, and transmissivity), and biotic community structure (total phototrophic biomass and size class). Picoeukaryote assemblage similarity was also strongly associated with water mass origin; assemblages in close spatial proximity (horizontally or vertically) showed less similarity if located in different water masses, while spatially distant assemblages showed higher similarity if located within the same water mass. This study highlights that ocean hydrodynamics must be considered to fully explain the distribution and diversity of microbes in this fluid realm.