Intermediate Water Flow Research Articles

Astronomically‐Paced Changes in Paleoproductivity, Winnowing, and Mineral Flux Over Broken Ridge (Indian Ocean) Since the Early Miocene

AbstractA significant shift in Earth's climate characterizes the Neogene, transitioning from a single‐ice‐sheet planet to the current bipolar configuration. This climate evolution is closely linked to changing ocean currents, but globally‐distributed continuous high‐resolution sedimentary records are needed to fully capture this interaction. The Ocean Drilling Program (ODP) Site 752, located on Broken Ridge in the Indian Ocean, provides such a Miocene‐to‐recent archive. We use X‐ray fluorescence (XRF) core scanning to build an eccentricity‐tuned age‐depth model and reconstruct paleoceanographic changes since 23 Ma. We find two intervals of enhanced productivity, during the early and middle Miocene (18.5–13.7 Ma) and late Pliocene/early Pleistocene (3–1 Ma). We also report a mixed eccentricity‐obliquity imprint in the XRF‐derived paleoproductivity proxy. In terms of grain size, three coarsening steps occur between 19.2–16 Ma, 10.8–8 Ma, and since 2.6 Ma. The steps respectively indicate stronger current winnowing in response to vigorous Antarctic Intermediate Water flow over Broken Ridge in the early Miocene, the first transient onset of Tasman Leakage in the Late Miocene, and the intensification of global oceanic circulation at the Plio‐Pleistocene transition. High‐resolution iron and manganese series provide a detailed Neogene dust record. This study utilized a single hole from an ODP legacy‐site. Nevertheless, we managed to provide novel perspectives on past Indian Ocean responses to astronomical forcing. We conclude that Neogene sediments from Broken Ridge harbor the potential for even more comprehensive reconstructions. Realizing this potential necessitates re‐drilling of these sedimentary archives utilizing modern drilling strategies.

Modeling of Water Transport through Plasmodesmata in Plant Cell

The water transport property in the plasmodesmata in a plant cell is calculated from the multiscale flow equation by incorporating both the adsorbed boundary layer flow and the intermediate continuum water flow. The plasmodesmata has the desmotubule which is the cylindrical nanotube with the diameter ranging between 20nm and 40nm and the length from 12000nm to 26000nm. In the absence of the wall slippage, there is the large flow resistance in this nanochannel preventing the water from flowing through; for the easy transport of water through this nanochannel,the wall slippage must occur and it results in the water flow rate through the channel several orders higher than the classical continuum flow theory calculation, depending on the power loss on the transportation. The pressure drop and the critical power loss on a single desmotubule for initiating the wall slippage are calculated as functions of the diameter and the length of the desmotubule.

Contourite stratigraphic models linked to the light intermediate versus dense deep Mediterranean water flow regime variations (Alboran Sea, SW Mediterranean)

Several water masses are involved in the circulation of oceans, their bottom layers impacting on sedimentation through contourites. The majority of palaeoceanographic studies on regional contourites are performed for one water mass despite that their joint study would offer relevant clues to understand past ocean and climate interaction. This works presents for the first time a an analysis about the impact of the Light Intermediate Mediterranean (LMW) and Dense Deep Mediterranean (DMW) bottom currents on the sedimentation in the Alboran Sea (SW Mediterranean) and its paleoceanographic significance in response to climatic oscillations from the last glacial period to the Holocene. To do this, an integration of chronostratigraphical, sedimentological, and compositional data is carried out from contourites formed by those water masses. That integration enable us to define three distinct contourite stratigraphic models. (I) The contourite terrace model, characterized by coarse-grained contourites, which is an archive of the interplay between the high-energy Atlantic Water-LMW interface and glacioeustasy from the Younger Dryas (YD) to the Holocene. (II) The contourite drift models, which are archives of rapid ocean-climate coupled fluctuations since 29.5 kyr. They comprise coarse-grained contourites formed by a relatively fast LMW and fine-grained contourites formed by a relatively weak DMW, except for the Heinrich Stadials HS3 to HS1 and YD when coarse-grained contourites were deposited. (III) The contourite/turbidite mixed model represents another archive of DMW and glacioeustasy interplay from the end of the late Pleistocene to Holocene.That contourite stratigraphy allows us to infer for the first time the relative variability of the LMW versus DMW flow regimes, which records differences and similarities. The similarities indicate that the LMW and DMW fluctuations occur in parallel at millennial and centennial time scales. The differences refer to the overall higher velocity of LMW versus DMW; the magnitude changes in velocities that are lower for LMW and higher for DMW; the recognition of three short ventilation events (a, b, c) during HS1 and HS2 for only DMW; and the distinct LMW and DMW responses to the onset of glacial conditions and return to interglacial conditions during the HSs, YD and Holocene cold periods.The proposed contourite stratigraphic models can be applied for other areas in the Mediterranean margins to identify and correlate the LMW and DMW palaeoceanographic events throughout this sea. The findings suggest that the different water masses that make up the water column must be seriously considered to fully understand palaeoceanographic and palaeoclimatic studies based on contourites. This is because their distinct impact on sedimentation may provide new insights into their different palaeoceanographic responses to rapid climatic oscillations and their triggering mechanisms.

Surface and thermocline ocean circulation intensity changes in the western Arabian Sea during ∼172 kyr

The relationship between monsoon-induced productivity and ocean circulation over millennial timescales is crucial. However, a study regarding the circulation of the western Arabian Sea (WAS) needs to be conducted. Understanding the seasonal, surface, and thermocline ocean circulation throughout the glacial-Interglacial period in the WAS is also elusive and essential. The long distant Antarctic Intermediate Water (AAIW) flow, and Sub-antarctic Mode Water (SAMW) penetration to the north side of the equator in the Indian Ocean needs to be understood and underlined using the micropaleontological (planktonic foraminiferal assemblages) and geochemical analysis such as oxygen isotope of Globigerinoides ruber and Neogloboquadrina dutertrei (δ18OG.ruber and δ18ON.dutertrei) in this study. Furthermore, understanding the variations in paleoproductivity, upper oceanic water column stratification, surface mixing, and thermocline layer variability in the WAS is also helpful. According to the results, the variation in the upwelling intensity during Glacial-Interglacial and monsoon variation suggest the upper water stratification/vertical mixing in the WAS. Here, we provide new evidence of poorly ventilated water mass in our region. Our results indicate that enhanced northward expansion of AAIW coincides with the weakening of summer monsoon during glacial periods except mid-MIS4, reflected by isotopic study and assemblages. In this context, depleted δ18ON. dutertrei value and high concentration of Globorotalia menardii (G. menardii) were due to lack/absence of AAIW ventilation and SAMW; therefore, warming occurred in the mid-MIS4.

Heat Transfer Characteristics of Cold Water Phase-Change Heat Exchangers under Active Icing Conditions

Under active icing conditions, the heat transfer performance of the CPHE has a significant impact on the system’s efficiency and energy consumption. Using the enthalpy-porosity method for describing the solidification process of liquids, the simulation and analysis of the effects of different parameter changes on the CPHE heat transfer performance were conducted to clarify the effects of the changes in the intermediary side inlet water temperature, intermediate water flow rate, and cold water flow rate on the heat transfer process in the CPHE. According to our results, changing the intermediary inlet water temperature has a greater impact on the heat transfer process in the cold-water phase-change heat exchangers. For every decrease of 0.5 °C in the intermediary side inlet water temperature, the average heat transfer coefficient increases by approximately 50 W/m2-K. Changes in the intermediary water flow rate affect the cold water phase-change heat exchanger’s heat transfer process. By increasing the intermediary water flow rate, the average heat transfer coefficient of a cold water phase-change heat exchanger can be improved, but the growth decreases, and the maximum flow rate of the intermediary water should not exceed 0.5 m per second. A change in the cold water flow rate in the cold water phase-change heat exchanger’s heat transfer process has a small impact on the cold water flow rate, increasing by 0.02 m/s each, with the average heat transfer coefficient increasing by 20 W/m2-K.

High-frequency modification of the central Mediterranean seafloor environment over the last 74 ka

Here we present a high-resolution record of benthic foraminiferal assemblages for the last 74 kyr from the Sicily Channel Ocean Drilling Program Leg 160 Site 963. Benthic foraminiferal results are compared with geochemical (benthic and planktic δ 18 O and δ 13 C) and calcareous plankton data, previously acquired on the same marine core sediments. Within the succession, three benthic foraminifera compositional zones were defined. Temporal changes in the assemblages are interpreted in the context of the modification of subtropical and temperate climate systems that affected the Mediterranean thermohaline circulation. A close connection between bottom conditions in the Sicily Channel and eastern Mediterranean Sea is evident in two intervals, characterized in the ODP Site 963 by reduced oxygen conditions. The first one, around 53–51 ka, is tentatively attributed to the ‘missing’ sapropel S2 while the second, between 35 and 29 ka, is marked by short and recurrent episodes of bottom-water oxygen decrease. Both are related to a weakening of the intermediate circulation in the Sicily Channel connected with relatively high northern hemisphere summer insolation and increase in Nile River discharge, which inhibited vertical mixing and intermediate water ventilation in Eastern Mediterranean Sea. Over the last deglaciation, the African humid period (AHP) and the sea level rise, also influenced the water mass structure in the Sicily Channel and a reduction of the bottom ventilation is suggested by a strong reduction of deep-water Miliolids. Decreased bottom oxygen levels, which testifies for a weakening of intermediate circulation in Sicily Strait, also characterized the interval corresponding to S1 deposition. Yet, the strong decrease of benthic foraminiferal abundance related to a low surface water trophic level, appears to be conditioned by the reduction of trophic levels in the western Mediterranean. The very high relative abundance of U. mediterranea recorded during this interval is explained by the availability of organic matter during a limited short year period and/or the availability of more degraded organic matter from river runoff. In general, compositional data analysis highlighted a quite complex response of benthic foraminifera to paleoclimatic changes. However, changes in the benthic foraminiferal assemblages recorded during the last glacial are coherent with surface paleoproductivity dynamics connected with D-O oscillation, and support oligotrophic, meso-eutrophic and oligo-mesotrophic conditions during the early interstadials, late interstadials and stadials, respectively. • High-resolution ODP963 (Sicily Channel) Last Glacial to Holocene benthic record. • Dansgaard-Oeschger imprints in bottom environments. • Connection between western and eastern Mediterranean dynamics. • Relationships between Levantine Intermediate Water flow and bottom ventilation.

A 51 ka sedimentary sequence in a seamount basin, Eastern Arabian Sea: Records for paleoceanographic and paleoclimate conditions

• Mineral magnetic parameters reveal the state of ocean ventilation and anoxia during the last 51 ka. • The MIS 3 monsoonal intensity regulated changes in detrital influx in the EAS. • Enhanced ocean-reducing conditions were reported during the Heinrich and deglaciation periods. A 5.4 m thick sediment core at ∼ 517 m water depth from a seamount basin off the Goa coast in the Eastern Arabian Sea (EAS) is examined for the mineral magnetic, carbonate and organic carbon variability. The 51 ka BP dated record is represented by Marine Isotope Stages (MIS) 3 to 1 under varying rates of sedimentation from 1.9 to 5.2 cm/ka. Comparison with records from adjacent cores for OC, TN, and CaCO 3 , this study indicates strong coupling of the seamount basin sedimentation with paleo-oceanographic conditions governed by southwest (SW) monsoon. The mineral magnetic parameters assigned three zones of variable paleo-oceanographic-paleoclimatic conditions marked by the interplay of high coercivity (oxidative) and low coercivity (reducing) mineralogy, that can be attributed to various factors including ocean ventilation governed by bottom water inflow of oxygen-depleted Sub-Antarctic Mode Waters and Antarctic Intermediate Water flows (SAMW-AAIW). This study emphasizes the significance of seamount basins as faithful recorders of long-term thermocline changes along with strong coupling to paleoceanographic conditions.

Lagged response of Tropical Atlantic Ocean to cold and fresh water pulse from Antarctic sea ice melting.

The formation of dense water masses at polar regions has been largely influenced by climate changes arising from global warming. In this context, based on ensemble simulations with a coupled model we evaluate the meridional shift of a climate signal (i.e., a cold and fresh water input pulse generated from melting of positive Antarctic sea ice (ASI) extremes) towards the Tropical Atlantic Ocean (TAO). This oceanic signal propagated from Southern Ocean towards the equator through the upper layers due to an increase in its buoyance. Its northward shift has given by the Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) flows, that inject cold and fresh mode/intermediate waters from into subtropical basin. The signal has reached low latitudes through the equatorial upwelling and spreads out southwards, through the upper branch of southern subtropical gyre. We concluded that 10 years of coupled simulations was enough time to propagate the climate signal generated by ASI positive extremes melting, which reached TOA around 2 year later. The oceanic connection between Southern Ocean and TAO is indeed established within the timescale analyzed in the study (10 years). Nonetheless, the period needed to completely dissipate the disturbance generated from ASI seems to be longer.

Along-Path Evolution of Biogeochemical and Carbonate System Properties in the Intermediate Water of the Western Mediterranean

A basin-scale oceanographic cruise (OCEANCERTAIN2015) was carried out in the Western Mediterranean (WMED) in summer 2015 to study the evolution of hydrological and biogeochemical properties of the most ubiquitous water mass of the Mediterranean Sea, the Intermediate Water (IW). IW is a relatively warm water mass, formed in the Eastern Mediterranean (EMED) and identified by a salinity maximum all over the basin. While it flows westward, towards and across the WMED, it gradually loses its characteristics. This study describes the along-path changes of thermohaline and biogeochemical properties of the IW in the WMED, trying to discriminate changes induced by mixing and changes induced by interior biogeochemical processes. In the first part of the path (from the Sicily Channel to the Tyrrhenian Sea), respiration in the IW interior was found to have a dominant role in determining its biogeochemical evolution. Afterwards, when IW crosses regions of enhanced vertical dynamics (Ligurian Sea, Gulf of Lion and Catalan Sea), mixing with surrounding water masses becomes the primary process. In the final part of the investigated IW path (the Menorca-Mallorca region), the role of respiration is further masked by the effects of a complex circulation of IW, indicating that short-term sub-regional hydrological processes are important to define IW characteristics in the westernmost part of the investigated area. A pronounced along-path acidification was detected in IW, mainly due to remineralization of organic matter. This induced a shift of the carbonate equilibrium towards more acidic species and makes this water mass increasingly less adequate for an optimal growth of calcifying organisms. The carbonate buffering capacity also decreases as IW flows through the WMED, making it more exposed to the adverse effects of a decreasing pH. The present analysis indicates that IW evolution in the sub-basins of the WMED is currently driven by complex hydrological and biogeochemical processes, which could be differently impacted by coming climate changes, in particular considering expected increases of extreme meteorological events, mainly due to the warming of the Mediterranean basin.

Diatomaceous ooze in a sedimentary core from Mariana Trench: implications for paleoceanography

Diatomaceous ooze sampled from near the Mariana Trench sediment surface by gravity corer (Core JL7KGC05) revealed a high sedimentary abundance of Ethmodiscus rex (Rattray, 1890) Wiseman and Hendey, 1953 fragments and tropical open ocean planktonic diatom taxa including Azpeitia nodulifera (Schmidt, 1878) Fryxell and Watkins in Fryxell, Sims and Watkins, 1986 and Alveus marinus (Grunow, 1880) Kaczmarska and Fryxell, 1996. Subsurficial sediments from the ooze are assigned a Marine Isotope Stage 2 age, approximately at the Last Glacial Maximum. The occurrence of Ethmodiscus ooze suggests massive late Pleistocene blooms in the Northwestern Pacific Ocean and provides a plausible link to paleoceanographic and paleoclimatic changes related to Antarctic Intermediate Water mass, which carried a high dissolved silica content as silicon leakage that reduced dissolution rate of diatom frustules. Northward flow of Antarctic Intermediate Water was probably related to surface current migration and southward shift of the Northwest Pacific Gyre to form oligotrophic conditions that triggered Ethmodiscus rex blooms under unusual nutrient recycling conditions within the ocean system. This bloom hypothesis may help explain differential silica dissolution during the last glacial stage.

Recent deep water ventilation in the South China Sea and its paleoceanographic implications

The South China Sea (SCS), being the largest marginal sea with high productivity in the western Pacific, was recently found to be a weak CO2 source based on the modern observation, probably caused by the vertical mixing of deep water within this basin. In order to reveal the distribution of apparent ventilation age of intermediate (water depth of 500–1500 m) and deep (water depth > 1500 m) waters and hence to explore deep water circulation in the SCS, the accelerator mass spectrometry (AMS) radiocarbon ages of co-existing benthic and planktic foraminifers from 13 surface and 4 core-top samples were measured. The results show that the recent deep water ventilation ages (Δ14CB-P ages) are between ~1790 and 2440 years in the northern SCS, comparable with the modern values of the deep western Pacific, implying the external impact of the penetration of Pacific Deep Water (PDW) across the Luzon Strait. Along the flow direction, the average ventilation ages decrease from ~1850 years to ~1330 years southward in the deep layer and from ~1600 years to ~1390 years northward in the intermediate layer. This phenomena may be attributed to the intra-basin well-ventilated process involving strong vertical deep mixing and advection. Our results not only validate the “sandwich” structure of deep water exchange between the SCS and Pacific: the deep water inflows from the western Pacific while the intermediate water flows out of the SCS, but also find the existence of the intermediate water with old carbon and low dissolved oxygen content in the southern SCS for the first time. Overall, the consistence of deep water ventilation ages with the physical-biogeochemical processes in the SCS is supported by the modern δ13C distribution of benthic foraminifers, further confirming that the deep circulation influences the CO2 release from the SCS to the atmosphere.

Intermediate water flows in the western South Pacific: as revealed by individual Argo floats trajectories and a model re-analysis

Abstract. Thanks to the autonomous Argo floats of the OUTPACE cruise (Oligotrophy to UlTra-oligotrophy PACific Experiment) and of the THOT (TaHitian Ocean Time series) project, some features of intermediate-flow dynamics, at around 1000 m depth, within the central and western South Pacific Ocean (around 19∘ S, 156∘ E–150∘ W) are described. In the Coral Sea, we highlight minima in dissolved oxygen of 140 µmol kg−1 that are associated with the signature of a southward transport of waters between two zonal jets: from the North Vanuatu Jet to the North Caledonia Jet. This transport takes place in the core of a cyclonic eddy or via the path between a cyclonic eddy and an anticyclonic one, highlighting the importance of mesoscale dynamics in upper thermocline and surface layers. Further east, we observe a strong meridional velocity shear with long-term float trajectories going either eastward or westward in the lower thermocline. More interestingly, these trajectories also exhibit some oscillatory features. Those trajectories can be explained by a single Rossby wave of 160-day duration and 855 km wavelength. Considering the thermohaline context, we confirm the meridional shear of zonal velocity and highlight a permanent density front that corresponds to the interface between Antarctic intermediate waters and North Pacific deep waters. Hence both circulation and thermohaline contexts are highly prone to instabilities and wave propagation.

Numerical Investigation into the Evolution of Groundwater Flow and Solute Transport in the Eastern Qaidam Basin since the Last Glacial Period

A complete understanding of groundwater circulation as well as the transport and distribution of solutes in arid-semiarid basin regions is a prerequisite for the safe use of groundwater resources. The distributions of the groundwater flow systema and solutes are affected by the basin morphology, lithology, and climate variations; therefore, they can change over geologic time. In this study, we performed a case study of the Qaidam Basin in the northeastern Tibetan Plateau, in which we utilized reactive solute transport simulations to build a numerical model in TOUGHREACT for a typical section of the eastern Qaidam Basin since the last glacial period. The results show that the groundwater in the eastern Qaidam Basin developed into a three-level groundwater flow system and that the seepage velocity of the local water flow system is significantly higher than that of the intermediate and regional water flow systems. Although groundwater in the discharge region has been continuously concentrated and enriched since the last glacial period, the distributions of the groundwater flow system and solutes have been greatly affected by climate variations. During warm periods, the centres of groundwater discharge and solute concentration shifted to areas with more groundwater recharge; in contrast, both centres shifted to the central basin during drought periods. The groundwater in the basin mainly contains Na+and Cl−ions, which vary significantly from the recharge region to the discharge region. Evaporation of groundwater results in increases in the concentrations of most of the components except HCO3−. The groundwater in the discharge region is currently in the stage of carbonate precipitation and is far from gypsum and halite precipitation.

Diel activity and foraging mode of juvenile Arctic charr in fluctuating water flow

AbstractStreams fluctuate in water flow because of natural (e.g., rain) and human‐induced events (e.g., hydropeaking). Magnitude, frequency, and predictability of these events can have drastic consequences for fish populations. We studied how rapid modifications of water flow affect diel activity and foraging mode of juvenile Arctic charr Salvelinus alpinus in stream enclosures exposed to either stable (intermediate) or fluctuating (low vs. high) water flow. Under stable conditions, Arctic charr showed limited activity (9.4%). In fluctuating water flow, charr increased activity during low flow periods, especially during the first hours after the flow decreased, but ceased activity almost completely at high flow. Charr were mostly nocturnal, and more nocturnal at low than intermediate water flow. Fish were more mobile and swam faster during prey search and attacked prey at longer distances at low water flow. Activity and foraging mode differed between the first and second day after reduced water flow, suggesting that Arctic charr require time to adjust their foraging behaviour. This study demonstrates the importance of behavioural flexibility for population ecology in fluctuating environments such as regulated rivers.

Seismic stratigraphy of upper Quaternary shallow-water contourite drifts in the Gulf of Taranto (Ionian Sea, southern Italy)

The occurrence of articulated seafloor morphology over continental shelf-upper slope environments, may result in a significant change in the patterns and intensity of basin-scale thermohaline circulation during eustatic sea-level fluctuations. These changes may cause, in turn, erosion, deposition and/or transport of sediments at the seafloor, to form shallow-water contourite drifts. Here we investigate this process in the NW sector of the Gulf of Taranto (Ionian Sea) during and following the Last Glacial Maximum (LGM), by integrating multibeam bathymetric data, ultra-high resolution seismic-reflection data and gravity core data. Sea level fall caused subaerial exposure of the summit of the Amendolara Bank, forming a short-lived island off the eastern coast of Calabria, and also creating a narrow passageway between the island and the northern Calabria mainland. Integrated seismic-stratigraphic data show that Upper Quaternary shallow-water contourite drifts and associated erosional features locally formed both around the flanks of the Amendolara Bank (AMBK), and the continental shelf and upper slope off the Amendolara village. Contourite drifts are bounded at the bottom and at the top by two major unconformities, indicating that the formation of the sediments drifts occurred between the onset of the LGM and the GS-1/Younger Dryas event. The stratal architecture suggests the occurrence of various types of contourite deposits, mostly represented by: a) Axial and lateral channel-patch drifts, and channel-related drifts along the incision to the NE of the AMBK; b) Sheeted drifts along the northeastern slope of the AMBK; c) Elongated drifts along the continental shelf and upper slope off the coast of Amendolara village. Erosional features also developed on the south-eastern flank of the AMBK, where the Levantine Intermediate Water flows from the central Ionian Sea towards the Gulf of Taranto, until the present-day. Both processes and timing responsible for erosion of the seafloor and the formation of sediment drifts in the Gulf of Taranto may be similar to that occurred in the Tyrrhenian margins during the Late Quaternary.

Palaeoceanographic and environmental changes in the eastern Fram Strait during the last 14,000 years based on benthic and planktonic foraminifera

Abstract Benthic and planktonic foraminifera, stable isotopes and other geochemical and sedimentological parameters have been investigated in a sediment core from Vestnesa Ridge (79°N, NW Svalbard margin, 1300 m water depth) in order to reconstruct the palaeoceanographic and palaeoenvironmental evolution of the eastern Fram Strait during the last 14,000 years. Our multiproxy data and, in particular, our high-resolution benthic foraminiferal record allow a detailed reconstruction of the intermediate water flow in the eastern Fram Strait. During the Bolling-Allerod warm interstadials the high proportion of the benthic Atlantic species Cassidulina neoteretis suggests the presence of chilled Atlantic-derived water at the bottom of the Vestnesa Ridge, while the dominance of the polar planktonic species Neogloboquadrina pachyderma (s) indicates cold polar surface conditions. During the Younger Dryas cold stadial the inflow of Atlantic-derived water was weakened and of lower temperature compared to the previous interval, as suggested by the increase in the glacio-marine indicator Cassidulina reniforme and the lower percentages of C. neoteretis. After 11,000 cal yr BP the abrupt increase in relative abundance of the benthic species Cibicides wuellerstorfi and Oridorsalis umbonatus, indicates a shift to interglacial conditions with deep convection and generation of cold intermediate water. Warm surface water conditions were finally established at about 10,300 cal yr BP, when Turborotalita quinqueloba became the dominant planktonic species. Generally warmer conditions than today were recorded in the middle Holocene, with a mild cooling at about 8200 cal yr BP and a more pronounced cool interval with an abrupt decrease in T. quinqueloba between 7000 and 6200 cal yr BP. Cold climatic conditions were established around 4100 cal yr BP when N. pachyderma (s) became again the dominant species and the polar benthic species Cribroelphidium excavatum appeared.

Simulating and mapping the spatial and seasonal effects of future climate and land -use changes on ecosystem services in the Yanhe watershed, China.

Effective information about ecosystem services is essential to help optimize and prioritize activities that support conservation planning in the face of land use and climate changes. This study shows an approach that integrates several dissimilar models for assessing water-related ecosystem services to predict values in 2050 under three land use scenarios in the Yanhe watershed. The simulated output variables pertaining to water yield and sediment yield were used as indicators for two ecosystem-regulating services, i.e., water flow regulation and erosion regulation, which were quantified using the soil and water assessment tool (SWAT) model. The model results were translated into a relative ecosystem service valuation scale, which facilitated the analysis of spatial and seasonal changes and served as the basis for the applied mapping approach. The simulated results indicate that higher water-related regulation services were concentrated in the middle and lower reaches of rivers with high water yield and low sediment erosion. The highest water flow regulation services occurred in summer; nevertheless, this was when erosion regulation services were the lowest compared to other periods in 2050. A comparison of the three land use scenarios showed differences in the water-related regulation services. Scenario 1, with high forest coverage, had the highest erosion regulation services, but the water flow regulation services were the lowest. Scenario 3 showed the reverse pattern. Scenario 2 had intermediate water flow regulation and erosion regulation. Increasing vegetation cover in the watershed is conducive to controlling water and soil erosion but could lead to a decline in available water resources. Spatial mapping is a powerful tool for displaying the spatiotemporal differences in the water-related regulation services delivered by ecosystems and can help decision makers optimize land use in the future, with the goal of maximizing the benefits offered by ecological services in the Yanhe watershed.

Foraminiferal proxy response to ocean temperature variability and acidification over the last 150 years in the Santa Barbara Basin (California)

The last 150 years on the California margin have been marked by high variability in precipitation, temperature, sea surface temperature, and ocean chemistry, in response to both natural and anthropogenic changes. Deciphering climate history from ocean sediments is dependent on our understanding of the various influences on marine proxies. Sediment from Santa Barbara Basin (SBB), California (box core SPR0901-10BC) provides an opportunity to compare multiple marine proxies with instrumental records of climate of the past 150 years and extend them beyond the historical record. Here we use three planktonic foraminiferal proxies, δ18Ocalcite, Mg/Ca, and size-normalized shell weight, to reconstruct the surface temperature and δ18Owater in SBB California at near-annual resolution from AD 1850–2000. Results indicate that Globigerina bulloides Mg/Ca reflects the instrumental temperature trends over the last 150 years, with average Mg/Ca temperatures approximately 2 °C lower than instrumental values, due to the slightly deeper habitat preference of G. bulloides. Similarly, temperature is the dominant control on G. bulloides δ18Ocalcite, and both Mg/Ca and δ18Ocalcite reflect variability consistent with changes in the intensification of ENSO over the past 150 years.Shell weights of the planktic foraminifer G. bulloides are inversely correlated with historical sea surface temperatures over the last 150 years in SBB sediments. Greater shell weight associated with cooler surface ocean temperatures does not support the anticipated relationship between coastal upwelling of cool, low pH water and shell thinning due to CO32− undersaturation. However, in contrast to the previous 130 years, G. bulloides shells deposited on the sea floor since the late 1970s exhibit a distinctive smooth shell structure indicative of partial dissolution. We hypothesize that a mid-1970s shift in intermediate water flow from predominantly equatorward to anomalously poleward led to the influx of relatively corrosive bottom water into SBB with subsequent carbonate dissolution at the sediment–water interface.

Holocene changes in Antarctic Intermediate Water flow strength in the Southwest Atlantic

Antarctic Intermediate Water (AAIW) is an essential component of the Atlantic meridional overturning circulation (AMOC) contributing to balance the southward flow of North Atlantic Deep Water (NADW). However, the role of AAIW in Holocene abrupt climate changes remains poorly understood. Here we reconstruct changes in the flow strength of AAIW based on a high temporal resolution paleocurrent record from the Southwest Atlantic. Superimposed on a slight increase in AAIW strength at ~7ka BP, a succession of millennial-scale AAIW variations is recognized in our paleocurrent records indicating a highly variable intermediate water circulation throughout the Holocene. Although variations in the strength and position of the Southern Westerlies Winds (SWW) are proposed to greatly influence the formation and circulation of AAIW, we cannot confirm such a potential SWW-AAIW linkage since our records of AAIW flow strength do not correlate to Holocene shifts of the SWW across the Atlantic. However, our data shows a good correspondence with abrupt variations in the AMOC with enhanced (reduced) northward advection of AAIW during periods of reduced (enhanced) NADW circulation. These results provide evidence for a Holocene AAIW-NADW see-saw. Thus, although the exact forcing mechanism remains unresolved, we suggest that Holocene perturbations in AAIW exerted a significant impact on the AMOC.

Habitat specialization and sensitivity to change in a threatened crayfish occupying upland streams

Abstract1. Crayfish are culturally and ecologically important species in freshwater ecosystems, but many are now threatened with extinction, due to threats such as habitat loss. Depending on their habitat selectivity and sensitivity, freshwater crayfish could provide effective targets for stream monitoring, restoration and conservation. This study used repeated field surveys of the threatened Murray crayfish, Euastacus armatus (family Parastacidae), to establish their habitat preferences and sensitivity to habitat loss across mesohabitat and microhabitat scales within upland streams of south‐east Australia.2. Selectivity analysis revealed that upland populations of E. armatus displayed a strong preference for areas of intermediate water flow velocity, deeper water, and stream beds dominated by boulders and gravel. Variations in E. armatus density among and within the two upland streams aligned with these microhabitat preferences, with best‐subsets analyses revealing that E. armatus abundance hotspots were best predicted by models combining water depth with percentage cover of boulders, gravel and overhanging riparian vegetation.3. Major shifts in stream habitat condition from 2009 to 2015 (e.g. 32% and 50% decline in boulder and overhanging vegetation cover, respectively) was associated with a 91% decline in E. armatus mean density within glide‐pool mesohabitats.4. These findings highlight how habitat specialization in threatened crayfish such as E. armatus may render them sensitive to changes in stream habitat condition, and how targeted monitoring, restoration and conservation of their preferred habitats could yield multiple benefits for montane freshwater ecosystems. Copyright © 2016 John Wiley & Sons, Ltd.