Westerly Wind System Research Articles

Satellite Observations of the Influence of Energetic Electron Precipitation on the Mesosphere and Stratosphere in the Northern Hemisphere

AbstractThe Earth’s atmosphere is influenced by energetic electrons coming from the magnetosphere. This energetic electron precipitation (EEP) is energized by the solar wind and directly affects in the high‐latitude mesosphere and lower thermosphere (MLT). EEP forms odd nitrogen (NOx) and hydrogen oxides (HOx) which destroy ozone. During winter EEP‐NOx descends to the stratosphere, establishing the indirect EEP effect. Several studies have found that EEP is related to changes in temperature and winds in the northern winter stratosphere. One of the most prominent effects of EEP is the influence on the northern polar vortex, a westerly wind system surrounding the winter pole in the middle atmosphere. Most studies of the EEP effect on dynamical features of the middle atmosphere have relied on either model simulations or reanalysis datasets which are mainly limited to stratospheric heights. We study here EEP effects on chemical and dynamical properties of the stratosphere and mesosphere in the northern hemisphere by using EOS Aura satellite’s measurements of atmospheric properties and POES satellites' measurements of precipitating electrons. We confirm earlier results showing that EEP decreases ozone and affects the temperature in the polar middle atmosphere and strengthens the stratospheric polar vortex. We show that EEP weakens the mesospheric polar vortex in late winter. This effect on polar vortex is partly due to changes in propagation and convergence of planetary waves. Accordingly, the EEP effect on the northern polar vortex depends on planetary waves not only in the stratosphere, as found in earlier studies, but also in the mesosphere.

Early Holocene permafrost retreat in West Siberia amplified by reorganization of westerly wind systems

Rapid permafrost degradation and peatland expansion occurred in Eurasia during the Early Holocene and may be analogous to the region’s response to anthropogenic warming. Here we present a 230Th-dated, multiproxy speleothem record with subdecadal sampling resolution from Kyok-Tash Cave, at the modern permafrost margin in the northern Altai Mountains, southwestern Siberia. Stalagmite K4, covering the period 11,400 to 8,900 years before present, indicates an absence of stable permafrost within three centuries of the Younger Dryas termination. Between 11,400 and 10,400 years ago, speleothem δ18O is antiphased between the Altai and Ural ranges, suggesting a reorganization of the westerly wind systems that led to warmer and wetter winters over West Siberia and Altai, relative to the zonally adjacent regions of Northern Eurasia. At the same time, there is evidence of peak permafrost degradation and peatland expansion in West Siberia, consistent with the interpreted climate anomaly. Based on these findings, we suggest that modern permafrost in Eurasia is sensitive to feedbacks in the ocean-cryosphere system, which are projected to alter circulation regimes over the continent.

Paleoproductivity Modes in Central Mediterranean During MIS 20—MIS 18: Calcareous Plankton and Alkenone Variability

AbstractPaleoproductivity is reconstructed across a Mediterranean benchmark record, the Early/Middle Pleistocene Montalbano Jonico section, cropping out in southern Italy. High‐resolution coccolithophore and alkenone data (C37 and C37:2/C38:2 ratio) were collected in order to extend the data set on Mediterranean paleoproductivity pattern and forcing mechanisms. The multi‐proxy record indicates low productivity during glacial and stadial phases and enhanced productivity during interglacial and interstadials. Increased surface water turbidity, cold‐water temperature and polar‐subpolar low salinity water incursion appear as the dominant controls for low productivity during Marine Isotope Stage (MIS) 20. Enhanced productivity during MIS 19c was sustained by warmer surface waters, coupled with a seasonal precipitation regime, providing higher nutrient availability. Productivity increases during interstadials with respect to stadials, in relation with enhanced land‐derived nutrient input through river discharge during wetter winters. The productivity scenario we propose is similar to those reconstructed from deep‐sea records in the central and western Mediterranean during Dansgaard‐Oeschger oscillations over the last 70 ka. This indicates that similar forcing mechanisms acted on productivity dynamics on a regional scale over different times. We suggest that migration of the westerly wind system over the Mediterranean and the polar water inflow influenced productivity on a regional scale. The acquired data set provides new evidences on the environmental significance of the C37:2/C38:2 ratio and on its relation with surface water productivity.

The Zealandia Switch: Ice age climate shifts viewed from Southern Hemisphere moraines

Two fundamental questions about the ice-age climate system await satisfactory resolution. First, if summer solar radiation intensity truly controls the orbital signature of the last glacial cycle, then why were major climatic shifts, including the last termination, globally synchronous? Second, what caused the millennial-scale climate oscillations superimposed on this cycle? We address these questions from a Southern Hemisphere perspective focused on mid-latitude mountain ice fields. We put particular emphasis on the last glacial termination, which involved both orbital-scale and millennial-scale climate elements and has generally well-resolved chronological control.Sustained retreat of mountain glaciers, documented by detailed mapping and chronology of glacial landforms in the Southern Alps and southern Andes, marked the termination of the last ice age, beginning ∼18 kyrs ago and involved a change from glacial to near-interglacial atmospheric temperature within a millennium or two. A rapid poleward shift of the Subtropical Front, delineating the northern margin of the Southern Ocean, ∼18 kyrs ago implies a concurrent poleward shift of the austral westerlies and leads us to hypothesize a southern origin for the dominant phase of the last glacial termination. Together with interhemispheric paleoclimate records and with results of coupled ocean-atmosphere climate modeling, these findings suggest a big, fast, and global end to the last ice age in which a southern-sourced warming episode linked the hemispheres. We posit that a shift in the Southern Ocean circulation and austral westerly wind system, tied to southern orbital forcing, caused this global warming episode by affecting the tropical heat engine and hence global climate.Central to this hypothesis, dubbed the ‘Zealandia Switch’, is the location of the Australia and Zealandia continents relative to Southern Hemisphere oceanic and atmospheric circulation. Coupled ocean-atmosphere climate modeling shows that the locus of the austral westerlies, whether in a more equatorward position representing a glacial-mode climate or in a poleward-shifted position marking interglacial-mode climate, has profound effects on oceanic and associated atmospheric linkages between the tropical Pacific and the Southern Ocean. Shifts in the austral westerlies have global climatic consequences, especially through resulting changes in the greenhouse gas content of the atmosphere and altered heat flux from the tropical Pacific into the Northern and Southern Hemispheres. We suggest that the last glacial termination was a global warming episode that led to extreme seasonality in northern latitudes by stimulating a flush of meltwater and icebergs into the North Atlantic from adjoining ice sheets. This fresh-water influx resulted in widespread North Atlantic sea ice that caused very cold boreal winters, thus amplifying the annual southward shift of the Intertropical Convergence Zone and the monsoonal rain belts. We further suggest that muted manifestations of the Zealandia Switch mechanism were responsible for smaller, recurring millennial-scale climate oscillations within the last glacial cycle.

A circumpolar dust conveyor in the glacial Southern Ocean

The increased flux of soluble iron (Fe) to the Fe-deficient Southern Ocean by atmospheric dust is considered to have stimulated the net primary production and carbon export, thus promoting atmospheric CO2 drawdown during glacial periods. Yet, little is known about the sources and transport pathways of Southern Hemisphere dust during the Last Glacial Maximum (LGM). Here we show that Central South America (~24‒32°S) contributed up to ~80% of the dust deposition in the South Pacific Subantarctic Zone via efficient circum-Antarctic dust transport during the LGM, whereas the Antarctic Zone was dominated by dust from Australia. This pattern is in contrast to the modern/Holocene pattern, when South Pacific dust fluxes are thought to be primarily supported by Australian sources. Our findings reveal that in the glacial Southern Ocean, Fe fertilization critically relies on the dynamic interaction of changes in dust-Fe sources in Central South America with the circumpolar westerly wind system.

E.M. van Zinderen Bakker (1907–2002) and the study of African Quaternary palaeoenvironments

The scientific contributions of E.M. van Zinderen Bakker (1907–2002) included the introduction of pollen analysis to Quaternary studies in South Africa. His palaeoecological theories evolved while performing palynological research in Southern Africa (the Maluti Mountains, Florisbad, Aliwal North, the Namib Desert), East Africa (Kalambo Falls, Mount Kenya, Cherangani Hills) and on the subantarctic islands (Marion and Prince Edward Islands). He was involved in the first radiocarbon dating from South Africa at Florisbad. Due to quantitative palynological studies he abandoned Wayland's (1929) Pluvial Theory that was generally accepted in the 1960s. He correlated observations of climate changes in Africa to data from marine borehole-cores and climatic fluctuations in the Northern Hemisphere. His observations led to the proposal that global temperature fluctuations are the primary cause of palaeoenvironmental changes. His studies culminated in a conceptual paleoecological model for the Last Glacial Maximum (LGM). Initially he based the model on symmetrical contraction of climatic belts about the equator that shifted the mid-latitude westerly wind system northward to increase the area receiving winter rainfall but later adjusted this by proposing a mechanism of westerly wind system intensification. He suggested that at this time grasslands had spread over wider areas in Southern Africa and that the tropical rain forests in the equatorial region fragmented. For interglacial periods he suggested that a southward shift of the Intertropical Convergence Zone (ITCZ) resulted in widespread humidity in the Congo Basin while large areas of the interior of Southern Africa became arid. Some of his ideas, especially his conceptual models of Quaternary vegetation and climate, are still relevant to the explanation of recent discoveries.

Winter precipitation changes during the Medieval Climate Anomaly and the Little Ice Age in arid Central Asia

The strength of the North Atlantic Oscillation (NAO) is considered to be the main driver of climate changes over the European and western Asian continents throughout the last millennium. For example, the predominantly warm Medieval Climate Anomaly (MCA) and the following cold period of the Little Ice Age (LIA) over Europe have been associated with long-lasting phases with a positive and negative NAO index. Its climatic imprint is especially pronounced in European winter seasons. However, little is known about the influence of NAO with respect to its eastern extent over the Eurasian continent.Here we present speleothem records (δ13C, δ18O and Sr/Ca) from the southern rim of Fergana Basin (Central Asia) revealing annually resolved past climate variations during the last millennium. The age control of the stalagmite relies on radiocarbon dating as large amounts of detrital material inhibit accurate 230Th dating. Present-day calcification of the stalagmite is most effective during spring when the cave atmosphere and elevated water supply by snow melting and high amount of spring precipitation provide optimal conditions. Seasonal precipitation variations cause changes of the stable isotope and Sr/Ca compositions. The simultaneous changes in these geochemical proxies, however, give also evidence for fractionation processes in the cave. By disentangling both processes, we demonstrate that the amount of winter precipitation during the MCA was generally higher than during the LIA, which is in line with climatic changes linked to the NAO index but opposite to the higher mountain records of Central Asia. Several events of strongly reduced winter precipitation are observed during the LIA in Central Asia. These dry winter events can be related to phases of a strong negative NAO index and all results reveal that winter precipitation over the central Eurasian continent is tightly linked to atmospheric NAO modes by the westerly wind systems.

A late Quaternary record of seasonal sea surface temperatures off southern Africa

The southern Cape coastal region is important for understanding both the behavioural history of modern humans, and regional and global climate dynamics, because it boasts a long archaeological record and occupies a key geographical location near the intersection of two major oceans. The western boundary Agulhas Current, implicated in global heat exchange dynamics, is an important modulator of southern African climates and yet we understand its past behaviour only broadly as the Current itself scours the coastal shelf and marine sediment core records necessarily provide little detail. Numerous archaeological sites from both the late Pleistocene and Holocene provide the opportunity for reconstruction of near-shore seasonal SST records, which respond both to localized wind-driven upwellings and Agulhas temperature shifts, corresponding in turn with terrestrial precipitation trends in the near-coastal and summer rainfall regions. Here we present a record of seasonal SSTs extending over MIS5, MIS4, and the Holocene, from serial δ18O measurements of a single gastropod species, Turbo sarmaticus. The results show that mean SST shifts accord well with global SST trends, although they are larger than those recorded in the Agulhas Current from coarser-scale marine sediment records. Comparison with a record of Antarctic sea-ice suggests that annual SST amplitude responds to Antarctic sea-ice extent, reflecting the positioning of the regional wind systems that drive upwelling dynamics along the coast. Thus, near-shore SST seasonality reflects the relative dominance of the westerly and easterly wind systems. These data provide a new climate archive for an important but understudied climate system.

Spatial and temporal variabilities of spring Asian dust events and their impacts on chlorophyll‐a concentrations in the western North Pacific Ocean

AbstractAs the western North Pacific Ocean is located downwind of the source regions for spring Asian dust, it is an ideal location for determining the response of open waters to these events. Spatial analysis of spring Asian dust events from source regions to the western North Pacific, using long‐term daily aerosol index data, revealed three different transport pathways supported by the westerly wind system: one passing across the northern East/Japan Sea (40°N–50°N), a second moving over the entire East/Japan Sea (35°N–55°N), and a third flowing predominantly over the Siberian continent (>50°N). Our results indicate that strong spring Asian dust events can increase ocean primary productivity by more than 70% (>2‐fold increase in chlorophyll‐a concentrations) compared to weak/nondust conditions. Therefore, attention should be paid to the recent downturn in the number of spring Asian dust events and to the response of primary production in the western North Pacific to this change.

Delayed hydrological response to Greenland cooling at the onset of the Younger Dryas in western Europe

During the Younger Dryas cold event about 12,800 years ago, environmental change in western Europe seems to occur 170 years after cooling over Greenland. Lake sediment analyses confirm this delay, and suggest European hydrological and vegetation change occurred only after the build-up of sea ice in the North Atlantic pushed the westerly wind system south.

Marine magnetic signature of the Last Glacial Maximum and last deglaciation from the Southern Hemisphere mid-latitudes

An environmental magnetic record is presented from piston core TAN0712-23, collected on the southern flank of Challenger Plateau at a water depth of 2817 m. Magnetic grain-size and concentration variations during the Last Glacial Maximum (LGM) are interpreted to reflect variations in terrestrial influx corresponding to glacial advance and stagnation events on millennial time-scales. The LGM signal between 25 and 23 ka demonstrates an antiphase relationship with Northern Hemisphere records implying that the bipolar seesaw was active during that period. The number and timing of features in TAN0712-23 suggest that LGM millennial scale climate fluctuations are strongly realized in the mid-latitudes, possibly due to amplification by regional forcing mechanisms. The onset of the deglacial magnetic signal, defined by a low concentration of magnetic minerals, is constrained at 18.6 cal ka BP by the radiocarbon age model and corresponds to southward migration of the Southern Hemisphere westerly wind system and Subtropical Front.

Long-term observations of saccharides in remote marine aerosols from the western North Pacific: A comparison between 1990–1993 and 2006–2009 periods

Anhydrosugars (galactosan, mannosan and levoglucosan), sugars (xylose, fructose, glucose, sucrose and trehalose) and sugar alcohols (erythritol, arabitol, mannitol and inositol) were measured in the aerosol samples collected in a remote island (Chichi-Jima, Japan) in the western North Pacific from 1990 to 1993 and from 2006 to 2009. Total concentrations of anhydrosugars, the biomass burning tracers, were 0.01–5.57 ng m−3 (average 0.76 ng m−3) during 1990–1993 versus 0.01–7.19 ng m−3 (0.64 ng m−3) during 2006–2009. Their seasonal variations were characterized by winter/spring maxima and summer/fall minima. Such a seasonal pattern should be caused by the enhanced long-range atmospheric transport of biomass burning products and terrestrial organic matter (such as higher plant detritus and soil dust) from the Asian continent in winter/spring seasons, when the westerly or winter monsoon system prevails over the western North Pacific. Sugars and sugar alcohols showed different seasonal patterns. The monthly mean concentrations of erythritol, arabitol, mannitol, inositol, fructose, glucose and trehalose were found to be higher in spring/summer and lower in fall/winter during both 1990–1993 and 2006–2009 periods, indicating an enhanced biogenic emission of aerosols in warm seasons. Interestingly, saccharides showed a gradual decrease in their concentrations from 1991 to 1993 and an increase from 2006 to 2009. In addition, the monthly averaged concentrations of sugars and sugar alcohols showed maxima in early summer during 1990–1993, which occurred about 1–2 months earlier than those during 2006–2009. Such a clear seasonal shift may be attributable to the changes in the strength of westerly and trade wind systems during two periods.

Spatial variability of Holocene changes in the annual precipitation pattern: a model-data synthesis for the Asian monsoon region

This study provides a detailed analysis of the mid-Holocene to present-day precipitation change in the Asian monsoon region. We compare for the first time results of high resolution climate model simulations with a standardised set of mid-Holocene moisture reconstructions. Changes in the simulated summer monsoon characteristics (onset, withdrawal, length and associated rainfall) and the mechanisms causing the Holocene precipitation changes are investigated. According to the model, most parts of the Indian subcontinent received more precipitation (up to 5 mm/day) at mid-Holocene than at present-day. This is related to a stronger Indian summer monsoon accompanied by an intensified vertically integrated moisture flux convergence. The East Asian monsoon region exhibits local inhomogeneities in the simulated annual precipitation signal. The sign of this signal depends on the balance of decreased pre-monsoon and increased monsoon precipitation at mid-Holocene compared to present-day. Hence, rainfall changes in the East Asian monsoon domain are not solely associated with modifications in the summer monsoon circulation but also depend on changes in the mid-latitudinal westerly wind system that dominates the circulation during the pre-monsoon season. The proxy-based climate reconstructions confirm the regional dissimilarities in the annual precipitation signal and agree well with the model results. Our results highlight the importance of including the pre-monsoon season in climate studies of the Asian monsoon system and point out the complex response of this system to the Holocene insolation forcing. The comparison with a coarse climate model simulation reveals that this complex response can only be resolved in high resolution simulations.

Middle- to late-Holocene environmental changes in Bajo de la Quinta, NE Patagonia, inferred by palynological records and their relation to human occupation

The north Patagonian region between 38° and 42°S extends along the proximity of two major atmospheric circulation features in South America: the northern border of the southern westerly circulation belt, and the northeast trade wind circulation associated with the subtropical South Atlantic Anticyclone. The influence of this westerly wind system determines the annual and seasonal precipitation regimen in north Patagonia, while the influence of the South Atlantic Anticyclone is more pronounced towards the east. The changing strength of either of these circulation systems has had a strong influence on Holocene environmental change in the region. Palaeoenvironmental changes are inferred from a 500 cm long core from Bajo de la Quinta, (40°55'42"S, 64°20'19"W) by means of pollen, sediment and geomorphological analyses. A dry phase with westerly winds during the middle Holocene, at around 7000–6600 cal. yr BP, is indicated by xerophytic/psammophytic vegetation and Patagonian steppe components. Between 6600 and 5200 cal. yr BP the pollen record reflects shrub steppe vegetation and low values of long distance transported pollen indicates little influence of the westerly winds. Between 5200 and 2900 cal. yr BP very arid conditions are indicated by high pollen values of Ephedra sp. and Nassauvia sp. and westerlies influenced by long distance pollen types such as Nothofagus sp. In the late Holocene (2900 cal. yr BP) the pollen record shows an increase in typical shrub taxa of the Monte and Espinal vegetation and low influence of long distance taxa. This may suggest a change to semi-arid conditions that persisted until the present, where the shrub steppe is the dominant vegetation. The environmental and geomorphological changes that occurred during the middle and late Holocene had influenced the space and resources used by hunter-gatherers of the area.

Evidence for climatic and oceanographic controls on terrigenous sediment supply to the Indian Ocean sector of the Southern Ocean over the past 63,000 years

Multiple proxy studies on sediment core SK 200/22a from the sub-Antarctic sector of the Indian Ocean revealed millennial-scale fluctuations in terrigenous input during the last 63,000 years. The marine isotope stages 1 (MIS 1) and MIS 3 are characterized by generally low concentrations of magnetic minerals, being dominated by fine-grained magnetite and titano-magnetite. Within the chronological constraints, periods of enhanced terrigenous input and calcite productivity over the last 63,000 years are nearly synchronous with the warming events recorded in Antarctic ice cores. An equatorward shift of the westerly wind system in association with a strengthening of the Antarctic Circumpolar Current (ACC) system may have promoted wind-induced shallow-water erosion around oceanic islands, leading to enhanced terrigenous input to the core site. Major ice-rafted debris events at 13–23, 25–30, 45–48 and 55–58 ka BP are asynchronous with δ18O and carbonate productivity records. This out-of-phase relation suggests that ice-sheet dynamics and ACC intensity were the primary factors influencing ice rafting and terrigenous input to the Indian sector of the Southern Ocean, with only limited support from sea-surface warming.

Sedimentary feature on Borsog Bay, eastern shore of Lake Khuvsgul in Northern Mongolia

Sedimentary feature on Borsog Bay, eastern shore of Lake Khuvsgul in Northern Mongolia This study reports on the sedimentary characteristics of Lake Khuvsgul which is located at the southern end of the Baikal Rift System within the continental interior of East Eurasia. With an elevation of 1645 m a.s.l., it has a climate that is mainly controlled by the Siberian-Mongolian high pressure system and the westerly wind systems from the Atlantic Ocean. Lake Khuvsgul, Mongolia's second largest lake by surface area (2760 km2), is the country's deepest fresh water lake with a bottom that is only 262 m a.s.l. Fed by 96 rivers and streams, it is drained by the Eg River which, after joining the Selenge River, flows into Lake Baikal. Analysis of a 12.3 m core from Borsog Bay near the eastern shore of the lake indicates a sedimentation rate of about 0.08 cm/a. It is believed that this relatively high sedimentation rate is due to the large sedimentary input from River Borsog and the variability of the turbidity currents at depths shallower than 9 m. It further suggests that the large sedimentation rate may be correlated with the annual and seasonal variations in the dominant westerly wind system over the Siberian Plateau. Such variations have resulted in a lowering of lake level and impacted the rate of erosion within the river's catchment area and therefore the sediment input to the lake. Because this is a preliminary report, further research into the sedimentary dynamics within Lake Khuvsgul and the role played in those dynamics by the climatic variability over Mongolia and Central Asia is planned.

Variability reduction through optimal combination of wind/wave resources – An Irish case study

This study presents a methodology to assess the possible benefits of the combination of wind energy with the still unexploited, but quite significant in Ireland, wave energy. An analysis of the raw wind and wave resource at certain locations around the coasts of Ireland shows how they are very low correlated on the South and West Coast, where the waves are dominated by the presence of high energy swells generated by remote westerly wind systems. As a consequence, the integration of wind and waves in combined farms, at these locations, allows the achievement of a more reliable, less variable and more predictable electrical power production. The resulting benefits are particularly clear in the case of a relatively small and quite isolated electrical system such as the Irish one. Here, in fact, high levels of wind penetration strongly increase the requirement of surplus capacity and cause a much lower efficiency for conventional thermal plants.

Rapid oceanic and atmospheric changes during the Younger Dryas cold period

The Younger Dryas event, which began approximately 12,900 years ago, was a period of rapid cooling in the Northern Hemisphere, driven by large-scale reorganizations of patterns of atmospheric and oceanic circulation 1‐3 . Environmental changes during this period have been documented by both proxy-based reconstructions 3 and model simulations 4 , but there is currently no consensus on the exact mechanisms of onset, stabilization or termination of the Younger Dryas 5‐8 . Here we present high-resolution records from two sediment cores obtained from Lake Krakenes in western Norway and the Nordic seas. Multiple proxies from Lake Krakenes are indicative of rapid alternations between glacial growth and melting during the later Younger Dryas. Meanwhile, reconstructed sea surface temperature and salinity from the Nordic seas show an alternation between sea-ice cover and the influx of warm, salty North Atlantic waters. We suggest that the influx of warm water enabled the westerly wind systems to drift northward, closer to their present-day positions. The winds thus brought relatively warm maritime air to Northern Europe, resulting in rising temperatures and the melting of glaciers. Subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice, which forced the westerly winds back to the south, cooling Northern Europe. We conclude that rapid alternations between these two states immediately preceded the termination of the Younger Dryas and the permanent transition to an interglacial state. The impact of freshwater pulses released from Northern Hemisphere ice sheets on the North Atlantic Meridional Overturning Circulation has been suggested as a likely mechanism for the Younger Dryas cooling 7 11 . In addition, a responsive sea-ice cover has been proposed as a mechanism that could rapidly alter the heat exchange between the ocean and atmosphere during the last glacial period 12,13 . The roles of the ocean and the atmosphere in triggering the climate shifts around the Younger Dryas are much discussed 9 . These hypotheses are difficult to resolve, partly because the temporal resolution of most palaeoclimate archives is too coarse to enable the anatomy of the Younger Dryas stadial to be adequately described 14 . To address these questions we here present a lake-sediment record at sub-annual resolution, together with new data on the sea-surface conditions of the Norwegian Atlantic Current(NwAC)throughouttheYoungerDryasstadial(Fig. 1).

Millennial-scale variability in the productivity signal from the Alboran Sea record, Western Mediterranean Sea

Primary productivity of the Alboran Sea (Western Mediterranean) is reconstructed for the time interval 48,000 to 28,000 years BP using the following geochemical proxies: calcium carbonate, barium excess (Ba excess), total organic carbon (TOC) and alkenone concentration. The records show a consistent pattern that indicates enhanced productivity during Dansgaard/Oeschger (D/O) warm periods. At the same time, deep-water conditions were favorable for organic matter preservation in the sediments, as indicated by the variation in redox-sensitive elements, such as Mn, Cr or V, and by the δ 13C record of benthic foraminifers. The Alboran Sea productivity variation during D/O cycles is explained by the succession of two climatic scenarios that led to latitudinal shifts of the westerly wind system. This mechanism would also account for the variability in the deep-water ventilation of the Western Mediterranean Sea.

Fluctuations of eolian flux and ocean productivity in the mid-latitude north Pacific during the last 200 kyr

In order to understand fluctuations in terrestrial and marine environments, a sedimentary core H3571 was investigated from the Hess Rise located in the mid-latitude North Pacific under the north westerly wind system. The δ 18 O , grain size and grain shape of type 1 quartz suggest that this quartz is of aerosol origin. Good correlation between Al and aerosol quartz in content and mass accumulation rate (MAR) indicates that the alumino silicate minerals in the sediments are mainly transported by wind. MAR of mineral aerosol (MAR Aerosol) varies from 156 to 732 mg cm −2 kyr −1 during the last 200 kyr. The MAR Aerosol maxima occur in oxygen isotope stage (OIS) 4 to latest OIS 5, middle OIS 6, moderate maxima occur in early OIS 1–2, late OIS 3 and middle OIS 3. These maxima are ascribed to reduced precipitation during the summer monsoon and to strengthened wind speed during the winter monsoon. The mean organic carbon/total nitrogen atomic ratio is 7.2, suggesting that the organic matter in the core H3571 is also mainly of marine origin. The MAR of organic carbon (MAR Organic) exhibits two prominent maxima in OIS 2 and 4 and relatively high values in middle and late OIS 6. Enhanced primary productivity is most likely to be responsible for the high burial rate of organic carbon in the sediments. Carbonate and phosphorus inputs with aerosol into sea surface have played a minor role through dissolution in diminishing PCO 2 in surface water during glacial times. On the other hand, the aerosol silica supply to the ocean may have some potential to affect the burial of biogenic silica into sediments. The effect of mineral aerosol on the ocean carbon cycle would be greater in the coastal and hemipelagic regions of the Western Pacific and Equatorial Atlantic, as compared with that in the Hess Rise regime.