Variability Of Water Masses Research Articles

Development of water-mass cluster analysis software to analyze the water-mass variations off the coast of Tohoku Japan: A case study for future application to analyze fisheries catch variation

Development of water-mass cluster analysis software to analyze the water-mass variations off the coast of Tohoku Japan: A case study for future application to analyze fisheries catch variation

Local Coastal Water Masses Control Heat Levels in a West Greenland Tidewater Outlet Glacier Fjord

AbstractFjords form the gateway between the open ocean and the Greenland Ice Sheet (GIS) and consequently play a crucial role for the stability of the Ice Sheet. Hydrographic observations, especially with seasonal resolution, from these fjords are limited making it difficult to assess linkages between the fjord, coastal water masses, and freshwater discharge from GIS. Here we present a decade‐long monthly hydrographic time series from a southwest Greenland fjord in direct contact with GIS. Our observations reveal significant temporal and spatial water mass variations related to coastal, glacial, and atmospheric dynamics. During winter, the fjord circulation is dominated by seasonal dense coastal inflows and the timing of these inflows determines intermediate and deepwater temperatures. During summer, runoff from GIS leads to a pronounced freshening of the fjord. In general, the fjord's seasonal circulation system damps the seasonal variation in temperature in the fjord. This leads to a seasonal temperature range in the intermediate layer in the inner part of the fjord that is half the observed range at the fjord entrance. Changes in mean water temperatures in the intermediate layer seem predominantly linked to local coastal water masses, where cold winter/warm summer events decrease/increase the mean water temperatures. Consequently, these events play an important role in heat transport toward glacier termini.

Simulation of Tsunami Impact on Water Mass Variations Based on Pareto Optimization

There is no query that the tsunami performs remarkable roles to alternate the physical properties of the ocean through mixing turbulent approaches. This study has proposed and demonstrated a new approach to retrieve the water mass pattern from remote sensing data. This examination has proposed and shown another way to deal with recovering water mass example from remote detecting information. The MODIS satellite information is procured pre, during and boxing day 2004.

Interannual changes in summer phytoplankton community composition in relation to water mass variability in the East China Sea

The surface distribution of the phytoplankton community was investigated in July 2009, 2010, 2011, and 2013 on the mid-shelf of the East China Sea (ECS), which is under the influence of Changjiang River Diluted Water (CDW) and the Kuroshio Current. This study, based on a CHEMTAX analysis of phytoplankton pigments, revealed a predominance of cyanobacteria and prochlorophytes in the eastern ECS, which is perennially under the influence of oligotrophic Kuroshio Surface Water. Towards the west, on the mid-shelf of the ECS, the composition of the phytoplankton community varied from year to year. Diatoms dominated in 2009 and 2013, when dissolved inorganic phosphate (DIP) concentrations were higher than during 2010 and 2011. During the latter two years, characterized as high-nitrate years, a mixed population of cyanobacteria, chlorophytes, and other groups was observed. Cluster analysis based on the phytoplankton community composition together with a PCA of shipboard hydrographic and nutrient data for all four years helped to confirm that the summer phytoplankton community structure of the ECS was regulated by the mixing of water masses and the variability of nutrient ratios within the CDW as it moved offshore. Our results show that elevated DIP concentrations in the CDW favor the growth of diatoms and dinoflagellates. The primary pathway for DIP inputs appears to be the upwelling of high-phosphate subsurface waters along the coast of China.

On the influence of Subtropical Mode Water on the South Atlantic Ocean

Abstract We investigate the spatiotemporal variability of the source water masses (i.e., varieties of Subtropical Mode Water – STMW) that contribute to the South Atlantic Central Water (SACW) in the South Atlantic Ocean. Thus, the composition of the SACW layer is updated. For this investigation, we applied an optimum multiparameter (OMP) analysis and used the conservative and semi-conservative parameters available from the World Ocean Database and Argo floats for the South Atlantic Ocean. The STMW18 (at upper levels) sourced in the central and eastern regions of the South Atlantic and the STMW12 (at lower levels) sourced at the boundaries of the South Atlantic Subtropical Front are the main contributors to the SACW. Although also important, the contribution of STMW14 (sourced in the Brazil-Malvinas Confluence zone) is regionally confined by the Brazil Current recirculation gyre. The contributions from Subtropical Indian Mode Water (SIMW) increased westward along the Agulhas Corridor, while the contribution from STMW12 decreased. The relatively low contribution from SIMW matches the results of previous studies regarding the influence of these waters in the climatology of the South Atlantic Ocean. However, it cannot be ignored, since the results bring new light to further investigations of the mixing processes in the ocean interior of the South Atlantic Ocean.

Biogeochemical patterns and microbial processes in the Eastern Mediterranean Deep Water of Ionian Sea

Microbial processes involved in water biogeochemistry are linked to physical and chemical variability of water masses. While the occurrence of hydrological changes in the Eastern Mediterranean Sea has been documented, its effects on microbial dynamics and processes have been poorly investigated. An interdisciplinary survey was carried out in November 2011 to depict recent scenarios in the Ionian Mediterranean Sea. This study provides a snapshot of the hydrology and biogeochemistry of this basin, with particular emphasis on the abyssal waters, where two cores of the Eastern Mediterranean Deep Water, both of Adriatic origin, were found. The first core, located at about 3000 m, overlies the second one, which has a recent origin. Both water masses have Adriatic origin and the upper one is older than the lower one. A novel approach has been adopted to relate changes in microbial abundance and metabolism to new thermohaline and biogeochemical findings. A close relationship between surface processes driven by air–sea interaction, microbial variables, physical and chemical parameters (nutrients, dissolved organic carbon and oxygen) was observed. Being intimately coupled to DOC patterns, the microbial respiratory activity was likely the most responsive microbial parameter to hydrological changes, confirming this variable as a sentinel of environmental changes.

A multiproxy study of the ocean-atmospheric forcing and the impact of sea-level changes on the southern Cape coast, South Africa during the Holocene

A multiproxy approach, focusing on biological proxies, was undertaken to determine the influence of sea-level changes along the southern Cape coast and the variability of water masses over the central Agulhas Bank region during the Holocene. A 30.47 m sedimentary core extracted from the coastal lake, Eilandvlei, shows continuous deposition for the last 9000 years. Microfossils were classified based on salinity and habitat, diatoms were further defined by their temperature preferences as either warm- or cold-water species. The composition of the assemblages is strongly linked to fluctuations in marine inflow into the system and the extent of freshwater inputs to the lake as recorded at the core site. Paleoproductivity improved during periods of equatorward migration of the westerlies, notably from 5800 to 5000 cal yr B.P., when surface water mixing increased. Spectral analysis revealed periodicities associated with solar cycles, namely Gleissberg and De Vries. The system remained predominantly marine and submerged in response to an early-mid Holocene transgression until 4700 cal yr B.P., when sea-level fluctuations and landscape modification restricted marine incursions, modified the exposed landscape and shifted the system toward a lagoon state. This multiproxy record provides insights into oceanic exchanges, surface water conditions and the mechanisms that govern them during the Holocene.

Sedimentary evolution of the Yangtze River mouth (East China Sea) over the past 19,000 years, with emphasis on the Holocene variations in coastal currents

Water mass variations in the early Yangtze estuary during the postglacial transgression have not been thoroughly studied. This research gap has hampered the understanding of riverine sediment ‘source to sink’ processes in this region. This study presents the results of integrated analyses of grain size, pollen-spore-dinocyst assemblages, benthic foraminifera and ostracods from a borehole, H5, located at the northern Yangtze mouth, to investigate the complete sedimentary history and associated variations in coastal currents since 19ka. At the core site, a fluvial floodplain developed from ca. 19–11.3ka, whereas an estuary to shelf to subaqueous delta prevailed during most of the Holocene. Based on changes in the dominant microfauna species, which mainly consist of Chinese coastal water species, two main current patterns were distinguished: one dominated by the Yellow Sea coastal current (YSCC) before ca. 7.9ka and one dominated by the Yangtze dilute water (YDW). Marked increases in open-sea saline species, including Bolivina robusta, and stratified water dinocyst species Spiniferites ramous and Spiniferites spp. were interpreted as the encroachment of the Taiwan warm current (TWWC) and the intensification of the YDW, respectively. The YDW and TWWC penetrated the area dominated by the YSCC before 7.9ka, which was likely related to intensity variations in the Kuroshio Current (KC) and Asian summer monsoon (ASM). Under maximal ASM and KC conditions, upwelling resulted from the intensified intrusion of the TWWC, as indicated by the blooming of Bolivina robusta from 7.9–6.3ka. After ca. 6ka, the YDW clearly weakened due to the decline of the ASM, yet the Yangtze plume prevailed due to the rapid seaward migration of the Yangtze mouth. Considering the dominance of the YSCC in the early Holocene, Yellow River-derived sediment likely represented a large proportion of the material delivered to the early Yangtze estuary.

Interannual variability of water masses in the area of bottom water formation in Рrydz Вay

The results of field studies of the processes of Antarctic Bottom Water formation conducted in the period from 2004 to 2016 in the Prydz Bay of the Commonwealth Sea is discussed. During this period the oceanographic observations along the 70° E section, crossing the shelf and the continental slope, were repeated nine times. In this area in the austral summer of 2004 during the AARI expedition on the r/v “Akademik Fedorov” the process of formation of bottom water has been recorded for the first time. A further study of the structure and characteristics of water masses on this section and in the adjacent area confirmed the regularity of these processes during the summer period. At the same time, a significant interannual variability of the structure, characteristics, and mechanisms of distribution of the main water masses in the section shelf, deep and bottom waters — was found. For the first time, detailed information on the bottom topography of the ocean in the vicinity of this section made it possible to show the determining role of bottom topography features in the distribution of newly formed bottom water along the continental slope. The tendency of increasing of the volume of bottom water formed in the Prydz Bay in recent years is revealed, which is associated with the intensification of the basal melting of the ice shelf leading to an increase in the volume of the formation of supercooled Shelf Water, the most important component in the formation of bottom water.

Seasonal variability of water masses and currents at the eastern Brazilian continental shelf (7.5–9[formula omitted] S)

The seasonal variability of water masses and currents of the Northeastern Brazilian continental shelf between 7.5-9∘ S are reported for the first time. Salinity and temperature data were collected during monthly hydrographic surveys between March/2012 and May/2013 across the shelf in the central part of the study area. Two broader surveys were carried out during winter (August/2013) and summer (January/2014) covering a total area of 4,600 km2. Water level and currents were also recorded with an acoustic Doppler current profiler (ADCP) moored near the mid-shelf (25 m) in the central area during the latter campaigns. The seasonal temperature variation ranged from 26 °C in September to 29.5 ∘C in April, with a two-month lag in respect to the minimum and maximum air temperature. The salinity did not present a clear seasonal variability, fluctuating between 36.5 and 37.0 psu throughout the year. The mean temperature and salinity from the campaigns in winter and summer were 26.5 and 27.6 ∘C and 37.1 and 36.7 psu, respectively. The Tropical Water (TW) was dominant, accounting for 95% to 97%, with presence of Coastal Water (CW) limited to the inner shelf. Colder waters were recorded at bottom along the shelf break indicating an upwelling process. The mean current speeds in winter and in summer were 0.11 and 0.06 m/s, respectively, reflecting the seasonal wind regime, more intense in winter. The currents in winter were predominantly northward, with short periods of southward inversions. These episodes were related with periods of along-shelf wind relaxation, potentially associated with atmospheric instabilities in higher latitudes. The currents during summer were sluggish and mainly southwards.

Mesoscale variability in the trophic ecology of the European hake Merluccius merluccius in the Strait of Sicily

The European hake Merluccius merluccius is one of the most important commercial species for the Mediterranean fisheries. In the Strait of Sicily, the species has some extended nursery areas, but its trophic ecology was not studied in detail, despite knowledge of the diet composition of fishes and their adaptability to food resource fluctuations is of major importance for the understanding of changes in fish abundance. In this study, we analyzed the trophic ecology of European hake by means of both stomach content and stable isotope analyses and correlated our results to environmental variables. According to both approaches, M. merluccius showed a clear ontogenetic shift in its diet with juveniles (70–160 mm total length (TL)) mostly relying on mysids and euphausiids, and adults (>160 mm TL) chiefly consuming larger prey, such as pelagic fish and decapods. Based on Spearman rank correlation (for isotopic tracers) and distance-based linear models (for diet), the trophic ecology of the species seemed to be mostly influenced by mesoscale variability of water masses in the Strait of Sicily, being latitude and longitude, temperature and salinity, among the most important explanatory variables. Further, fluorescence, as a proxy of primary production, was an explanatory variable likely enhancing zooplankton availability and in turn affecting M. merluccius diet.

Forcing mechanisms and hydrodynamics in Loch Linnhe, a dynamically wide Scottish estuary

Hydrodynamic conditions in Loch Linnhe, a dynamifcally wide estuary on the west coast of Scotland, are primarily influenced by wind forcing, freshwater input, and tides. Winds in the region are orographically steered along the axis of the estuary due to surrounding mountains. A large rainfall catchment area results in a large freshwater inflow into Loch Linnhe which in turn produces low salinity waters at the head of the estuary. This, combined with a connection to the open sea with coastal salinities, leads to salinity gradients in the horizontal and vertical. Even though a range of observational programmes have focussed on Loch Linnhe, the literature still lacks an evaluation of its physical dynamics. Here we present a first description of the hydrodynamics in Loch Linnhe based on observations. Wind stress predominantly influences the surface layer, especially at low frequencies and with a stronger influence than tides during neap tides. The buoyancy-driven flow due to the large river runoff influences the circulation independent of wind stress. Seasonal (spring, autumn) and interannual (2011, 2012) variability of water masses occur especially in the surface layer. Tides are dominated by the semi-diurnal constituent M2 with tidal ellipses aligned in the along-estuary direction and a stronger influence during spring tides compared to wind. An evaluation of dimensionless numbers reveal laterally and vertically sheared exchange flows. Compared to other Scottish estuaries Loch Linnhe is wide enough to be influenced by the Earth's rotation and demonstrates an enhanced freshwater outflow along its north-western coast as the freshwater is diverted to the right in the direction of the flow. These observed patterns are important for the sustainable environmental management of this socio-economically valuable region, e.g. through their relevance to aquaculture pathogen transmission patterns. A thorough understanding of the dynamics of the system is essential for a successful evidence-based marine planning framework.

Semi‐quantitative reconstruction of early to late Holocene spring and summer sea ice conditions in the northern Barents Sea

ABSTRACTSemi‐quantitative estimates of early to late Holocene spring sea ice concentration (SpSIC) and occurrence of summer sea ice for the northern Barents Sea have been obtained by analysing the biomarkers IP25, brassicasterol and a tri‐unsaturated highly branched isoprenoid lipid in a Holocene marine sediment core. Sub‐surface water mass variations were derived from planktic foraminiferal assemblages and stable isotopes (δ18O, δ13C). The record indicates paleoceanographic changes over three intervals. During Period I (ca. 9500–5900 cal a BP), the study location experienced the lowest recorded SpSIC (ca. 25%) with short spring seasons and long productive summers, resulting partly from increased Atlantic Water inflow that caused a stronger ocean–atmosphere heat exchange. Throughout Period II (ca. 5900–2700 cal a BP), the winter sea ice margin migrated southwards and an overall cooling trend resulted in higher SpSIC (ca. 60%) and increased delivery of cold Arctic Water. During Period III (ca. 2700 cal a BP to present), SpSIC increased further (ca. 75%) and some sea ice remained during summer months. A sub‐surface warming probably indicates a decoupling of heat exchange between the ocean and the atmosphere. Longer springs and shorter summers were accompanied by the most southerly location of the winter sea ice margin.

Global mean sea level variations and the land water cycle at the inter-annual scale during the 2014–2016 El Niño episode

Since 1993, the global mean sea level (GMSL) has been rising at a rate of about 3 mm/a detected by multi-satellite radar altimetry. The spaceborne gravimetry satellite, Gravity Recovery and Climate Experiment (GRACE), has been monitoring Earth’s surface water mass variations since 2002. La Nina and El Nino events induces inter-annual variations of the GMSL manifest in ocean mass and steric sea level changes, linked with corresponding changes in land water cycle. Here we study the GMSL inter-annual variations and global land water mass changes integrating satellite altimetry, GRACE and Argo data, 2010–2016, during which strong La Nina and El Nino events occurred. First, we quantify the evolutions of GMSL during the study time period. The results show that during the 2010–2011 La Nina episode, the GMSL dropped rapidly to 7.6 mm, with the ocean mass and the steric sea level decreased to 5.1 mm and to 1.8 mm, respectively. GMSL then increased to 19.2 mm, with ocean mass increased to 12.3 mm during 2011–2013. From 2013 to 2014, the steric GMSL increased by 2.1 mm, and the ocean mass variations dropped by 2.3 mm, thus the total GMSL remains nearly unchanged. During the strong 2014–2016 El Nino, ocean mass variations increased by 13.1 mm and contributed over 90% of GMSL change, which rises up by 15.1 mm. Next, we analyze land water mass changes in four regions, namely Australia and Southeast Asia, South America, North America, Antartica and Greenland, and investigate their linkage to the GMSL inter-annual variations. Here, we used the Forward Modelling (FM) method for GRACE data post-processing to reduce signal leakage problem to estimate land water storage mass changes. The results show that during the 2014–2016 El Nino episode, the global ocean mass increasing is mainly due to the total land water storage decreasing in Australia and Southeast Asia, South America, and Antartica and Greenland. The inter-annual variations of global ocean mass variation during 2003–2016 is closely linked with the land water storage changes from Australia and Southeast Asia and the South America regions, which are strongly affected by La Nina and El Nino events. During 2003–2016, the ice ablations from the Antartica and Greenland ice sheets directly contributed to GMSL rising, as opposed to the land water mass increase in the North America region, which has a negative effect on GMSL trend. Finally, we estimated the GMSL, ocean mass and steric sea level trends at 3.4±0.4, 2.1±0.3, and 1.1±0.2 mm/a, respectively during 2003–2016, and 6.5±1.2, 4.1±1.0, and 1.9±0.4 mm/a, respectively during 2010–2016. We concluded that the ocean mass variation contributed to the GMSL trend two times larger than that of the steric sea level contribution during these two time periods. However the ocean mass variation is roughly equivalent to the steric sea level variation during 2003–2010.

Measuring pH variability using an experimental sensor on an underwater glider

Abstract. Autonomous underwater gliders offer the capability of measuring oceanic parameters continuously at high resolution in both vertical and horizontal planes, with timescales that can extend to many months. An experimental ion-sensitive field-effect transistor (ISFET) sensor measuring pH on the total scale was attached to a glider during the REP14-MED experiment in June 2014 in the Sardinian Sea in the northwestern Mediterranean. During the deployment, pH was sampled at depths of up to 1000 m along an 80 km transect over a period of 12 days. Water samples were collected from a nearby ship and analysed for dissolved inorganic carbon concentration and total alkalinity to derive the pH for validating the ISFET sensor measurements. The vertical resolution of the pH sensor was good (1 to 2 m), but stability was poor and the sensor drifted in a non-monotonous fashion. In order to remove the sensor drift, a depth-constant time-varying offset was applied throughout the water column for each dive, reducing the spread of the data by approximately two-thirds. Furthermore, the ISFET sensor required temperature- and pressure-based corrections, which were achieved using linear regression. Correcting for this decreased the apparent sensor pH variability by a further 13 to 31 %. Sunlight caused an apparent sensor pH decrease of up to 0.1 in surface waters around local noon, highlighting the importance of shielding the sensor from light in future deployments. The corrected pH from the ISFET sensor is presented along with potential temperature, salinity, potential density anomalies (σθ), and dissolved oxygen concentrations (c(O2)) measured by the glider, providing insights into the physical and biogeochemical variability in the Sardinian Sea. The pH maxima were identified close to the depth of the summer chlorophyll maximum, where high c(O2) values were also found. Longitudinal pH variations at depth (σθ > 28. 8 kg m−3) highlighted the variability of water masses in the Sardinian Sea. Higher pH was observed where salinity was > 38. 65, and lower pH was found where salinity ranged between 38.3 and 38.65. The higher pH was associated with saltier Levantine Intermediate Water, and it is possible that the lower pH was related to the remineralisation of organic matter. Furthermore, shoaling isopycnals closer to shore coinciding with low pH and c(O2), high salinity, alkalinity, dissolved inorganic carbon concentrations, and chlorophyll fluorescence waters may be indicative of upwelling.

Influence of curing protocols on water sorption and solubility of a self-adhesive resin-cement

Aim: To evaluate the effect of different activation protocols on the polymerization of a self-adhesive dual cured resin-based cement. Methods: Thirty disc-shaped specimens were prepared with the resin cement RelyX U200 (3M ESPE) and divided according to three protocols: immediate light-activation for 40 s, delayed light-activation (10 min after manipulation, for 40 s) or self-curing without light-activation. The specimens were desiccated, kept in water at 37 °C for 7 days and desiccated again to calculate water sorption, solubility and mass variation. Data were analyzed by Shapiro-Wilk Test and Wilcoxon tests (α=0.05). Images after the specimens’ final desiccation were also made. Results: The Wilcoxon test revealed a significant difference for sorption and mass variation (p<0.05) and the highest value was observed in self-curing or chemical activation group (CA), followed by delayed light-activation (DL) and immediate light-activation (IL). Besides the water sorption parameters, there were also microvoids on the discs from the delayed and no light-activation groups. Conclusions: The light-activation immediately after manipulation is recommended for the evaluated resin cement.

Surface hydrographic and water mass variability in the eastern equatorial Pacific during interglacial-like Marine Isotope Stage 14

Surface temperature and water masses variability in the Eastern Equatorial Pacific (EEP) is sensitive to global climate changes in response to either Northern/Southern Hemisphere forcing or low-latitude atmosphere-ocean feedback. High-latitude processes can influence tropical oceans via atmospheric bridges and oceanic tunnels, whereas perturbations in the low-latitude atmosphere-ocean modulate the behavior of low-latitude oceans. For climate paradoxes of prolonged warmth MIS (Marine Isotope Stage) 15–13, little has known about any causes or any possible tele-connections between the EEP and high-/low-latitudes because lack of observations. To address this issue, multiple sea surface temperature (SST) records (i.e. faunal transfer function-based, Mg/Ca ratio on mono-species, and Uk’37-derived temperature estimates) and faunal-derived water masses are generated from the EEP core ODP 1240. Our results reveal a glacial EEP MIS 14 cooling (∼1–2 °C) with higher eastern boundary current faunal abundances as compared to adjacent interglacial stages. In a glacial MIS 14 scenario, we suggest that the EEP areas would receive more nutrient-rich, cold waters from high latitudes via the Peru-Chile Current. The atmospheric bridge of a northwardly Intertropical Convergence Zone (ITCZ) shift and the resulting heat/moisture transport across the eastern equatorial Atlantic (EEA) would weaken the magnitude of the EEP cold tongue in MIS 14. We also think of another scenario in that the orbital variations in glacial MIS 14 was characterized by higher obliquity fluctuations, lower eccentricity/precession. The orbital variations shape an inter-hemispheric asymmetry with higher seasonality. This scenario could result in a stagnant/an inactive Atlantic Meridional Ocean Circulation and northward shifts in the ITCZ/southward displacement of westerlies in the southeastern Pacific during MIS 14. The retreat of the West Antarctic sea ice and enhancement of the Antarctic Circumpolar Current would also bring less high-latitude cold upwelled water (the Subantarctic Mode Water/Antarctic Intermediate Water) into the eastern tropical Pacific/Atlantic Oceans. We suggest that a diminished La Nina-like condition and a relatively weakened EEP/EEA cold tongue developed in glacial MIS 14 compared to other glacial MIS in the late Quaternary. The interglacial-like MIS 14 is therefore characterized by a small-magnitude of eastern tropical upwelling areas and greater extension of western Pacific/Atlantic warm surface waters. Such amplifications in glacial MIS 14 could lead to less fluctuation of Termination VI and persistent warmth in MIS 15–13.

Evaluation of GRACE Mascon Gravity Solution in Relation to Interannual Oceanic Water Mass Variations

With evidence of an accelerated water cycle over the past few decades, we make inferences on the spatial variability of interannual evaporation and precipitation patterns from 2003 to 2014 gravity anomalies, using the Gravity Recovery and Climate Experiment (GRACE) satellite mascon data set. Comparison of the mascon solution with an ensemble harmonic solution is conducted, along with validation over the oceans via sea surface height from multimission altimetry minus Argo floats data/GECCO2 [the GECCO2 ocean synthesis is the German contribution to Estimating the Circulation and Climate of the Ocean project ( www.ecco-group.org )] steric sea level. The mascon solution was consistently more accurate than its spherical harmonic counterpart across large spatial and temporal scales, due mainly to the inherent smoothing from the mascon cells. Comparison of GRACE with both GECCO2 + altimetry and Argo + altimetry mass estimates revealed an offset in phase with regard to the annual cycle, but yielded an rmse of only 5.6 mm in the interannual signal after phase correction. This paper furthers evidence of an accelerated water cycle at a rate of 1.5% ± 1.1% at low latitudes, and provides a means of validation for oceanic freshwater budget studies based on salinity measurements.

Upper water mass variability in the Anegada–Jungfern Passage, NE Caribbean, during the last 11,100 cal. yr

Using qualitative and quantitative analyses of planktonic foraminifera assemblages, δ18O measurements, Mg/Ca–temperature relationship ( Globigerinoides ruber pink sensu stricto) data and sea-surface temperatures (SSTs) derived from artificial neural network (ANN) transfer functions, a reconstruction was made of upper water mass variability in the Anegada–Jungfern Passage (AJP), northeastern Caribbean Sea, over the last c. 11,100 years. Our record is based on the study of two marine sediment cores and reveals three main circulation stages during the Holocene. In the early-Holocene (11,100–6300 cal. yr BP), ANN-based SST estimations indicate moderately cooler than present winter condition in the NE Caribbean with SSTs of ~25.5°C. These conditions presumably reflect advection of well-mixed upper water masses from the Guyana upwelling area associated with a strong Atlantic Meridional Overturning Circulation (AMOC) and enhanced trade wind activity, linked to a more northerly location of the inter-tropical convergence zone (ITCZ). Between 6300 and 3700 cal. yr BP, a relative warming of winter SSTs (~26.5°C) was probably related to a weaker circulation and upper water mass mixing because of less intense trade wind activity, as the ITCZ moved southwards. From 3700 cal. yr BP to the present, the region was characterised by small seasonal SST variations and generally stable winter and summer SSTs. The data suggest a minor shift in the (sub)surface inflow pattern during the last 2000 years, possibly related to changes in Northern Hemisphere large-scale atmospheric circulation also observed at higher latitude. The ANN-based temperature pattern is supported by fluctuations in the Mg/Ca-derived temperature record, although temperature maxima derived from the Mg/Ca ratio appear anomalously high. On a Holocene timescale, we conclude that the northeastern Caribbean SST and circulation regime have been mainly dependent on the position of the ITCZ, which, in turn, is controlled by changes in hemispheric solar insolation.

Hydrological variations of the intermediate water masses of the western Mediterranean Sea during the past 20 ka inferred from neodymium isotopic composition in foraminifera and cold-water corals

Abstract. We present the neodymium isotopic composition (εNd) of mixed planktonic foraminifera species from a sediment core collected at 622 m water depth in the Balearic Sea, as well as εNd of scleractinian cold-water corals (CWC; Madrepora oculata, Lophelia pertusa) retrieved between 280 and 442 m water depth in the Alboran Sea and at 414 m depth in the southern Sardinian continental margin. The aim is to constrain hydrological variations at intermediate depths in the western Mediterranean Sea during the last 20 kyr. Planktonic (Globigerina bulloides) and benthic (Cibicidoides pachyderma) foraminifera from the Balearic Sea were also analyzed for stable oxygen (δ18O) and carbon (δ13C) isotopes. The foraminiferal and coral εNd values from the Balearic and Alboran seas are comparable over the last ∼ 13 kyr, with mean values of −8.94 ± 0.26 (1σ; n = 24) and −8.91 ± 0.18 (1σ; n = 25), respectively. Before 13 ka BP, the foraminiferal εNd values are slightly lower (−9.28 ± 0.15) and tend to reflect higher mixing between intermediate and deep waters, which are characterized by more unradiogenic εNd values. The slight εNd increase after 13 ka BP is associated with a decoupling in the benthic foraminiferal δ13C composition between intermediate and deeper depths, which started at ∼ 16 ka BP. This suggests an earlier stratification of the water masses and a subsequent reduced contribution of unradiogenic εNd from deep waters. The CWC from the Sardinia Channel show a much larger scatter of εNd values, from −8.66 ± 0.30 to −5.99 ± 0.50, and a lower average (−7.31 ± 0.73; n = 19) compared to the CWC and foraminifera from the Alboran and Balearic seas, indicative of intermediate waters sourced from the Levantine basin. At the time of sapropel S1 deposition (10.2 to 6.4 ka), the εNd values of the Sardinian CWC become more unradiogenic (−8.38 ± 0.47; n = 3 at ∼ 8.7 ka BP), suggesting a significant contribution of intermediate waters originated from the western basin. We propose that western Mediterranean intermediate waters replaced the Levantine Intermediate Water (LIW), and thus there was a strong reduction of the LIW during the mid-sapropel ( ∼ 8.7 ka BP). This observation supports a notable change of Mediterranean circulation pattern centered on sapropel S1 that needs further investigation to be confirmed.