A 350-ky radiolarian record off Lüderitz,Namibia—evidence for changes in the upwelling regime

The study of radiolarian assemblages from Core MD 962086 provides new information on the variability in the upwelling intensity and origin of upwelled water masses over the past 350 ky in one of the major filamentous regions of the Benguela Upwelling System (BUS), located off Lüderitz, Namibia. The use of key radiolarian species to trace the source of upwelled waters, and the use of a radiolarian-based upwelling index (URI) to reconstruct the upwelling intensity represent the first use of radiolarians for paleoceanographic reconstructions in the BUS. These radiolarian-based proxies indicate strongest upwelling during Marine Isotope Stages (MIS) 3, 5, and 8, which compares well with other studies. While during MIS 3 and 8, the radiolarian-based proxies indicate the influx of waters of Southern Ocean origin, they also point to the increased influence of tropical waters during the lower portion of MIS 5. During MIS 2, 4 and 6 the radiolarian assemblages indicate generally lower upwelling intensities, although this signal is complicated by the increased occurrence of organic carbon in the sediments during these intervals. During MIS 2 there appears to be less of an input of Southern Ocean waters to the BUS, although during the also glacial MIS 4 and 6, there is evidence for an increased influence of cold Antarctic waters. The comparison of the results from Core MD 962086 with other studies in the BUS area indicates a non-uniform pattern of upwelling intensity and advection of cold, southern waters into this system during MIS 2. Weaker upwelling signaled by the radiolarian-based proxy in MIS 4 is in contrast to other studies that indicate higher productivity during this time period. In general, the data show that there is a strong spatiotemporal complexity in upwelling intensity in the BUS and that the advection of water into it is not strongly tied to glacial–interglacial variations in climate.     

Late Quaternary paleoproductivity and deep water circulation in the eastern South Atlantic Ocean: Evidence from benthic foraminifera

Two late Quaternary sediment cores from the northern Cape Basin in the eastern South Atlantic Ocean were analyzed for their benthic foraminiferal content and benthic stable carbon isotope composition. The locations of the cores were selected such that both of them presently are bathed by North Atlantic Deep Water (NADW) and past changes in deep water circulation should be recorded simultaneously at both locations. However, the areas are different in terms of primary production. One core was recovered from the nutrient-depleted Walvis Ridge area, whereas the other one is from the continental slope just below the coastal upwelling mixing area where present day organic matter fluxes are shown to be moderately high. Recent data served as the basis for the interpretation of the late Quaternary faunal fluctuations and the paleoceanographic reconstruction.

During the last 450,000 years, NADW flux into the eastern South Atlantic Ocean has been restricted to interglacial periods, with the strongest dominance of a NADW-driven deep water circulation during interglacial stages 1, 9 and 11. At the continental margin, high productivity faunas and very low epibenthic δ¹³C values indicate enhanced fluxes of organic matter during glacial periods. This can be attributed to a glacial increase and lateral extension of coastal upwelling. The long term glacial-interglacial paleoproductivity cycles are superimposed by high-frequency variations with a period of about 23,000 yr. Enhanced productivity in surface waters above the Walvis Ridge, far from the coast, is indicated during glacial stages 8, 10 and 12. During these periods, cold, nutrient-rich filaments from the mixing area were probably driven as far as to the southeastern flank of the Walvis Ridge.     

High frequency palaeoceanographic changes during the past 140?000 yr recorded by the organic matter in sediments of the Iberian Margin

Biogenic records of the marine palaeoproductivity (carbonates, organic carbon, and C₃₇ alkenones) and the molecular stratigraphy of past sea surface temperatures (SSTs; U₃₇^K′) were studied at high resolution in two cores of the Iberian Margin. The comparison of these records indicates that the oceanographic conditions switched abruptly during the past 160 kyr between three kinds of regimes. A first regime with high (17-22°C) SST and low productivity typifies the interglacial periods, marine isotopic stages (MIS) 5 and 1. Several periods during MIS 6, 2, and the terminations II and I are characterised by about 4-5°C colder SST and a higher organic matter accumulation, both of which define the second regime. This anticorrelation between SST and marine productivity suggests that these variations are related to the intensity of the coastal upwelling. By contrast with this upwelling behaviour, extremely low biological productivity and very cold SST (6-12°C) occurred during short phases of glacial MIS 6, 4, and 2, and as abrupt events (≈1 kyr or less) during MIS 3. The three oceanographic regimes are consistent with micropalaeontological changes in the same cores based on foraminifera and diatoms.The general trend of these hydrologic changes follows the long-term glacial/interglacial cycle, but the millennium scale variability is clearly related to Heinrich events and Dansgaard-Oeschger cycles. Strengthening of the upwelling corresponds probably to an intensification of the subtropical atmospheric circulation over the North Atlantic which was influenced by the presence of continental ice sheets. However, extreme glacial conditions due to massive discharges of icebergs interrupted the upwelling. Interestingly, both terminations II and I coincided with strong but transient intensification of the upwelling.     

Radiolarian and sedimentologic paleoproductivity proxies in late Pleistocene sediments of the Benguela Upwelling System,ODP Site 1084

The changing composition of radiolarian faunas from late Neogene deep-sea sediments has been used in recent years as a proxy for changes in marine paleoproductivity. We examine radiolarian faunas, organic carbon content (TOC), opal and coarse-fraction components over the last 270,000 years in sediments from ODP Hole 1084A, drilled in a high productivity upwelling region within the Benguela Upwelling System off the west coast of Africa. Age control is provided by stable oxygen isotope measurements of benthic foraminifera. Prior research has established that late Pleistocene glacial intervals in this upwelling system generally had higher productivity than interglacials. The radiolarian WADE (water-depth ecology) paleoproductivity index correlates well with TOC and opal in these samples, and all three parameters change in synchrony with the benthic isotope curve over all but the MIS 5e–6 time interval. WADE inferred productivity is significantly higher in glacials than interglacials. We conclude that the WADE index is a useful proxy for paleoproductivity at this location, as are also opal and organic carbon accumulation rates. Carbonate and carbonate based indices such as the accumulation rate of benthic foraminifera (BFAR) by contrast do not correlate well either to productivity indices or to the glacial–interglacial cycle, and are interpreted to primarily reflect carbonate dissolution.     

Reconstruction of Indian monsoon variability over the past 230,000 years: Planktic foraminiferal evidence from the NW Arabian Sea open-ocean upwelling area

We determined the faunal composition and total number of tests (#/g) of planktic foraminifera (> 125 μm) in core KH00-05 GOA 6 near Oman in order to decipher monsoon-induced variability of oceanographic productivity in the open-ocean upwelling area in the northwest Arabian Sea. The core contains a continuous record of sedimentation over the last 230 kyr, with the age model based on oxygen isotope and accelerator mass spectrometry ¹⁴C dates. We focused on species (Globigerina bulloides and Globigerinita glutinata) typical for SW monsoonal upwelling and species typical for NE monsoon conditions (Neogloboquadrina incompta, Neogloboquadrina dutertrei, Globigerinoides ruber, and Globigerinoides sacculifer). The changes in relative abundance of these monsoonal indicators suggest that the open-ocean upwelling area was dominated by the SW monsoon during interglacial periods, but by the NE monsoon during glacial periods.Increases in total test abundance during glacial periods confirmed that the NE monsoon rather than SW monsoon contributes largely to planktic foraminiferal productivity in this area. We argue that three types of circumstances resulted in high productivity, with nine high productivity events occurring at a 23-kyr frequency. The first type caused high productivity events at 102 and 199 ka (interglacial periods), characterized by the dominance of upwelling species, indicating high productivity during strong SW monsoons, correlated with high July insolation at 45° N. An exceptional high productivity event occurred at 37 ka during interglacial marine isotope stage (MIS) 3, with contributions from both SW and NE monsoons. The second type of high productivity event occurred at 61, 147, and 175 ka, during glacial periods, characterized by dominance of NE monsoon species, and correlated with low January insolation at 45° N. In addition, a high productivity event at 85 ka (interglacial period) also was induced by enhanced NE monsoons. The last two high productivity events occurred during transitional periods from glacial to interglacial (MIS 6/5.5 and 2/1), were characterized by the replacement of NE monsoon species with upwelling species, and corresponded to abrupt climate warming, suggesting that they are related to both accelerated SW monsoon systems and reduced NE monsoon systems.     

Paleoenvironmental changes in northwest Mongolia during the last 27?kyr inferred from organic components in the Lake Hovsgol sediment core record

We studied organic components in the X106 sediment core (length 130.3 cm, water depth 236 m, 50°53′01″N, 100°21′22″E) from Lake Hovsgol to elucidate the biological production, source of organic components, and paleoenvironmental and paleolimnological changes during the last 27 kyr in northwest Mongolia. Total organic carbon (TOC) contents (0.20–0.70%) in the core of the last glacial period increased dramatically and attained 3.16–5.85% in the postglacial period (Holocene), together with the increase of the contribution of terrestrial organic matter. Biological production (both terrestrial and aquatic production) based on the TOC contents in the Holocene was 14 times higher than that in the last glacial period. The B?lling-Aller?d warm period and Younger Dryas cool period were both observed at depths of 55–50 cm (ca. 15–13 cal kyr BP) and 50–45 cm (ca. 13–11 cal kyr BP), respectively. We propose here a terrestrial/aquatic index (TAI) for organic matter in lake sediments. The TAI values suggest that terrestrial organic matter in the bottom of the core was less than 10%, increased to 48% in the B?lling-Aller?d warm period, decreased abruptly to 20% in the Younger Dryas cool period, and again increased to 30–40% in the Holocene. Normal-C₃₁ alkane (a biomarker of herbaceous land plants) and n-C₁₈ alkanoic acid (marker of plankton) decreased from the last glacial period to the Holocene, whereas n-C₂₃ alkane and n-C₂₂ alkanoic acid (a marker of higher vascular plants) increased from the last glacial period to the Holocene. Scarce herbaceous plant vegetation, such as Artemisia spp. of the lake basin in the last glacial period, changed into an abundance of higher woody plant vegetation (e.g., Pinus spp., Betula spp. and/or Larix spp.) in the Holocene. Stanol/sterol ratios suggest that relatively high oxygen tension of the lake bottom in ca. 27–22 cal kyr BP decreased from this age to the present, though benthic organisms are still abundant.     

Distribution of ostracod and benthic foraminiferal assemblages during the last 550 kyr in the East-Corsica basin,western Mediterranean Sea: A paleo-environmental reconstruction

The study of Quaternary sediments covering the last 550 kyr from the borehole GDEC-4-2, East-Corsica basin, was performed through the study of benthic meiofaunal assemblages (ostracoda and benthic foraminifera) whose distribution responds to climate changes, and glacial–interglacial variability in particular. The interglacial ostracod group is mainly composed of the Argilloecia acuminata, Cytheropteron alatum, Henryhowella sp., Polycope sp. and Cytherella sp., which indicate an enhanced surface productivity and possibly high bottom water temperature during these warm intervals. Benthic foraminifera, such as Hoeglundina elegans, Sigmoilopsis schlumbergeri, Bigenerina nodosaria and Hyalinea balthica are predominant during interglacial periods and also show an increasing surface productivity associated to warm intervals. Increase in surface productivity would contribute to an enhanced export of organic matter to sea floor at the GDEC-4-2 site during interglacial periods. The bottom temperature drop coupled with the important sedimentary inputs (associated to a significant quantity of refractory organic matter) during glacial periods was highlighted by the predominance of ostracoda, such as Paradoxostoma sp., Cytheropteron testudo, Bathycythere vanstraateni, Macrocypris sp., Echinocythereis echinata and benthic foraminifera as Bolivina spathulata, Bulimina costata, and Bulimina marginata. The distribution of some benthic foraminifera species describing a turnover system allowed the characterization of the last three climate cycles (MIS 8–9, MIS 6–7, MIS 1–5) probably marked by changes of bottom water paleoceanographic conditions in terms of temperature, salinity, bottom current intensity and surface productivity. The cyclic variations of the allochthonous group recorded over the last 550 kyr suggest a major role played by the eustatic factor, with the latter possibly favouring down slope transport. The distribution of this group allowed thus establishing a link between shelf-basin sediment transfer and climate, with enhanced shelf-basin sediment transfer during glacial low stands.     

Latest Eocene–Early Oligocene climate change and Southern Ocean fertility: inferences from sediment accumulation and stable isotope data

The earliest Oligocene (∼33.5 Ma) is marked by a major step in the long-term transition from an ice-free to glaciated world. The transition, characterized by both cooling and ice-sheet growth, triggered a transient but extreme glacial period designated Oi-1. High-resolution isotope records suggest that Oi-1 lasted for roughly 400,000 yr (the duration of magnetochron 13N) before partially abating, and that it was accompanied by an ocean-wide carbon isotope anomaly of ∼0.75‰. One hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate-induced intensification of wind stress and upwelling, particularly in the Southern Ocean. To understand how this climatic event affected export production in the Southern Ocean, biogenic silica (opal) and carbonate accumulation rates were computed for the sub-polar Indian Ocean using deep-sea cores from ODP Site 744, Kerguelen Plateau. Our findings suggest that net productivity in this region increased by several fold in response to the Oi-1 glaciation. In addition, calcareous primary producers dominant in the Late Eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the Southern Ocean. We attribute these changes to intensification of atmospheric/oceanic circulation brought about by high-latitude cooling and the appearance of a full-scale continental ice-sheet on East Antarctica. Higher terrigenous sediment accumulation rates support the idea that wind-induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro-nutrients (e.g., iron-rich dust particles). We speculate that the rapid changes in biogenic sediment accumulation in the Southern Ocean and other upwelling-dominated regions contributed to the ocean-wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon. The changes in burial rates, in turn, may have produced a positive feedback on climate by briefly drawing down atmospheric p_CO2.     

贝加尔湖-钻孔(BDP 96-1)的孢粉分析

贝加尔钻探计划（BDP）中的96－1井位于贝加尔湖中央的科学湖脊,1996年冬从位于332m水深以下的钻井采样,钻孔从湖底向下深2000m,根据古地磁资料,钻孔年代推测为5．1Ma,Tsuga,Lepidobalanus,Ulmaceae,Tilia和Corylus发现于钻孔的下部约60m,因为这些化石花粉目前在贝加尔湖地区已经消失,说明该钻孔上部的气候比下部的冷,因此,第四纪的气候比晚第三纪的更为干冷。在亚北极的西伯利亚,冰期时期以草本植物花粉占统治地位,花粉浓度较低,而在间冰期时期以木本花粉为主,花粉浓度较高,在间冰期时期硅藻及有机物总量增加,潮湿度（wet density)及氧同位素比率都降低,相反,在冰期时期硅藻含量及有机物总量降低,而潮湿度（wet dendity)和氧同位素比率都增加。     

Sensitivity of south‐east Atlantic planktonic foraminifera to mid‐Pleistocene climate change

Abstract: The last one million years are important in terms of climate development during the so‐called Mid‐Pleistocene Transition when amplification of the glacial–interglacial cycles occurred. This study describes abundance changes in fossil planktonic foraminifera in sediments from Core T89‐40, retrieved from the Walvis Ridge in the south‐east Atlantic, across this time period. Cycles between upwelling and subtropical planktonic foraminiferal assemblages are shown to mirror changes between glacial and interglacial periods, respectively. During interglacial marine isotopic stages (MIS) 9, 11 and 31, however, anomalously high abundances of the polar left‐coiled Neogloboquadrina pachyderma occur, presumably linked to unusual seasonal upwelling waters. The planktonic foraminiferal abundance record shows 41‐ky cyclic variations in the regional oceanography linked to cycles in insolation influenced by changes in the Earth’s axial tilt (obliquity). These orbitally induced oscillations in oceanographic change occurred throughout the entire record. The most conspicuous feature of the planktonic foraminiferal record is the near absence of left‐coiled Globorotalia truncatulinoides between 960 and 610 ka (MIS 26‐15). The abrupt disappearance of this species is synchronous with the onset of the Mid‐Pleistocene Transition in MIS 26.     

Changes in style and intensity of production in the Southeastern Atlantic over the last 70,000 yr

Accomplishing reliable paleo-reconstructions of productivity and upwelling conditions in eastern boundary current systems requires the use of cores collected in a basin-wide spatial pattern. Based on diatom assemblage analysis and the concentration and the bulk biogenic components of three gravity cores recovered from the Benguela Upwelling System (BUS) between 19° and 25°S, I describe rapid paleoceanographic changes that occurred during the last 70 ka B.P. in the southeastern Atlantic. The pattern of biogenic production and accumulation differs to varying degrees among the three core sites along the SW African coast. The highest sedimentation and accumulation rates at 25°S off Lüderitz conform with the present-day, well-known pattern of highest productivity and most intense coastal upwelling. Highest diatom values at 25°S during MIS3 points to more intense upwelling due to the combination of strong seaward-extending upwelling filaments, shoaling of the upwelled water, and the influence of silicate-rich waters of Antarctic origin. Productivity decreased along the central BUS throughout MIS2, when the siliceous–calcareous productivity regime shifted toward a system dominated by calcareous producers. Although intensity and strength of winds created adequate conditions for upwelling during MIS2, diatom production decreased. The complete replacement of the upwelling-associated diatom flora by a non-upwelling-related diatom community during MIS1 reflects weakened upwelling, weakened seaward extension of the upwelling filaments, and dominance of warmer surface waters. Combining changes in the composition of the diatom assemblage and variations of the bulk biogenic components allows for reliable reconstruction of paleoproductivity and upwelling changes for the SE Atlantic during the last 70 ka B.P.     

Export of DOM from Boreal Catchments: Impacts of Land Use Cover and Climate

Dissolved organic matter (DOM) is an important fraction in carbon (C) and nutrient budgets for aquatic ecosystems and can have broad effects on food webs and nutrient cycling. To look at the role land use cover and climate might play in DOM transport from the boreal region, the export of total organic carbon (TOC), total organic nitrogen (TON) and dissolved organic phosphorus (DOP) was estimated for Finnish main rivers and their sub-catchments, altogether 86 catchments, situated between latitudes 60° N and 69° N and covering 297,322 km², 88% of the total area of Finland. On an average, 94% of the TOC, 90% of the total nitrogen (TN) and 40% of the total phosphorus (TP) in Finnish rivers was in a dissolved form. The majority of the DOM export from Finnish catchments consists of organic C. The TOC export increased with increasing peatland proportion (r = 0.39, p = 0.003), while TON export increased with the increasing percentage of agricultural land (r = 0.60, p <0.001). Although upstream lakes covered only on average 9% of the catchment area, they were the most important predictor for TOC, TON and DOP export (r = −0.83, r = −0.82 and r = −0.61, respectively). The higher the upstream lake percentage, the lower the export indicating organic matter retention in lakes.     

Tasman Front shifts and associated paleoceanographic changes during the last 250,000 years: foraminiferal evidence from the Lord Howe Rise

The paleoceanography of the Tasman Sea over the past 250,000 years was studied using benthic (>75 μm size fraction) and planktonic foraminifera (>149 μm size fraction) from three cores collected along 162°E traverse between 25°S and 30°S on the Lord Howe Rise. Planktonic foraminiferal oxygen isotope stratigraphy dates the cores between OIS 1 and 11. R-mode cluster and Q-mode factor analyses were carried out on benthic foraminiferal faunas, and Q-mode factor analysis and the modern analog technique (MAT) were used in analyzing planktonic foraminiferal faunas. Distinct benthic faunas across latitude from north (25°S) to south (30°S and 35°S) reflects the difference in primary productivity level in the overlying surface water. The MAT result is thought to express latitudinal shifts of the Tasman Front over the last 250,000 years with: (1) the Tasman Front at 35°S during the oxygen isotope stage (OIS) 1 (post-glacial period); (2) migration of the front nearby 25°S during the last glacial period (OIS 2–OIS 4) and slightly northward of its present position during the penultimate glacial period (OIS 6); and (3) a return of the front to near 35°S during OIS 5 and OIS 7. Based on time-series and spatial variations of benthic foraminiferal factor typified by Pseudoparrella exigua and Uvigerina peregrina and one variety, southern-winter mixing and convection along the Tasman Front may have strengthened during the interglacial OIS 7 in particular.     

Significance of ocean carbonate budgets for the global carbon cycle

Changes in the trace gas composition of the atmosphere over glacial–interglacial cycles are linked to changes in the oceanic carbon cycle. This paper examines the role of biologically driven fluxes of organic and inorganic carbon in modifying the carbon dioxide chemistry of the oceans, and the corresponding implications for the partitioning of CO₂ between the atmosphere and ocean. Relevant details of the marine carbon system are presented together with an assessment of the significance of remineralization and dissolution processes. Recent estimates of the marine carbonate fluxes show significant uncertainties and inconsistencies which must be resolved in order to assess fully the role of the oceans' biota in the marine carbon system. Various types of ocean carbon cycle models have been developed in order to interpret the changes in past atmospheric carbon dioxide. Some take account of the role of the oceans' biota, focussing in the main on the cycling of organic matter. Relatively few have considered the role of the carbonate pump and the subtle interactions between organic and inorganic carbon cycling. The significance of carbonate formation and dissolution, and of the effects of global change on the marine carbonate system, for air–sea fluxes of CO₂ are discussed. Finally some recommendations for future research are made in order to improve our understanding of how spatial and temporal variation in marine carbonate fluxes, in conjunction with processes determining the oxidation and burial of organic matter in the oceans, affect levels of CO₂ in the atmosphere.     

Characterization of organic matter in cross-margin sediment transects of an upwelling region in the Campos Basin (SW Atlantic, Brazil) using lipid biomarkers

Lipid biomarkers [fatty acids (FAs), sterols and alcohols] and total organic carbon (TOC) were analyzed in 48 surface (0–2 cm) sediment samples collected twice (winter 2008/2009 and summer/2009) in two transects ranging from 25 to 3,000 m depths. This sampling array encompassed the major upwelling region in the southeastern Brazilian continental margin, where the river influence is probably minimal. The objectives were (1) to evaluate the sources, transport and major areas of organic matter (OM) accumulation in the continental margin and (2) to identify the fraction of OM that is potentially available to secondary benthic producers. As expected from the regional oceanographic characteristics, lipids derived from primary and secondary autochthonous producers (0.073–5.3 mg gTOC^?1) made the major fraction of the sedimentary OM, whereas lipids from allochthonous sources (0.043–0.40 mg gTOC^?1) and from bacteria (<0.01–0.43 mg gTOC^?1) were of relatively less importance. The accumulation of OM in the sediments was highly dependent on the coupling of physical (hydrodynamics) and biological (response to upwelling) factors. It was found that while some restricted areas in the shelf was a sink of labile OM, the export of this material to the upper and middle slope (400–1,000 m depths) can represent an important source of bioavailable OM to the deep sea benthic community.     

The variation of upper ocean structure and paleoproductivity in the Kuroshio source region during the last 200 kyr

A core from the source region of the Kuroshio warm current (east of the Luzon Island) was analyzed using several proxies in order to study the variability of the Western Pacific Warm Pool (WPWP) during the last two glacial–interglacial cycles. Primary productivity (PP) variations were deduced from variations in the coccolith flora. Primary productivity was higher during glacial periods (the end of Marine Isotope Stage [MIS] 3, some periods in MIS 2 and 6), and decreased during interglacial periods (MIS 7, MIS 5e and probably MIS 5c–5d), with the lowest PP in MIS 5e. Variations in the δ¹³C difference in benthic and bulk carbonate, thus in the vertical gradient of δ¹³C in dissolved inorganic carbon (Δδ¹³C_{C. wuellerstorfi–N. dutertrei} and Δδ¹³C_{C. wuellerstorfi–coccolith}) coincided with the PP changes, showing that export productivity was low during interglacial periods (MIS 7, MIS 5e and Holocene) and high during glacial periods (MIS 6, probably MIS 5c–5d, late MIS 4 and late MIS 3). Comparison of foraminiferal carbonate dissolution indicators and PP changes reveals that nannofossil assemblage in core Ph05-5 is not sensitive to carbonate dissolution intensity. The depth of the thermocline (DOT) was estimated from planktonic forminiferal assemblages, and was relatively greater during interglacial periods (MIS 7, MIS 5e, probably MIS 5c and Holocene) than during glacials (middle MIS 6, probably MIS 5b and 5d, some periods in MIS 4, MIS 3 and MIS 2). Good coherence between the paleoproductivity records and the DOT suggests that the DOT changes could be the primary control factor in changes of paleoproductivity, and the glacial high productivity in the Kuroshio source region could be associated with a global increase of nutrient concentration in the intermediate waters that upwelled into the photic zone. The low CO₂ values derived for intervals of high productivity and a relatively shallow DOT suggest that the changes in biological productivity and DOT in the equatorial Pacific could have modified atmospheric CO₂ concentrations. High Sea Surface Temperatures (SSTs) during the warm MIS 5e in combination with intensified monsoonal rain fall could have resulted in a more intense stratification of the upper waters, resulting in low nutrient supply to the surface waters and a resulting decrease in productivity.     

Decreasing organic carbon bioreactivity in European rivers

1. European rivers experience increased loading of total organic carbon (TOC) from terrestrial sources due to factors involving changes in land use, climate and soil acidity. However, little is known about how increased TOC is linked to changes in the bioreactivity of organic matter in these rivers on a continental scale.
2. We compiled paired measurements of TOC and biological oxygen demand in 5-day 20°C dark incubations from 3,486 EU monitoring rivers. Assuming first-order decay and a fixed respiratory quotient, annual average TOC and biological oxygen demand values were used to calculate 11,060 values of the decay coefficient k.
3. The k decreased by two orders of magnitude as a power function of increasing TOC. This relationship could partly be explained by carbon quality, as the C:N ratio of the organic matter was the lowest in high-reactivity low-TOC rivers, and vice versa. A trend analysis showed that TOC increased by 18% from 1996 to 2012, while k decreased by as much as 50%. As a consequence, the biological oxygen demand in the water decreased over time in spite of the water browning trend (increased TOC).
4. Together, these results suggest that reactivity is low near terrestrial hot spots for TOC export, and low during years with high terrestrial TOC loading, but increases in rivers with low TOC concentrations where internal processes in the water have high relative influence on bulk TOC quality. Thus, browning of European freshwaters is linked to strong decreases in TOC reactivity on a continental scale, suggesting that the impacts of browning on microbial water deoxygenation and greenhouse gas production are less severe than previously thought.

     

PLEISTOCENE EXTINCTIONS OF DEEP-SEA BENTHIC FORAMINIFERA: THE SOUTH ATLANTIC RECORD

Abstract:  Sixty-two species and 19 genera of elongate, cylindrical benthic foraminifera disappeared from the deep-sea in the south-east Atlantic (ODP Sites 1082 and 1083) and the Atlantic sector of the Southern Ocean (ODP Site 1088) during the Early and Middle Pleistocene as part of the global extinction of the families Pleurostomellidae, Stilostomellidae and portions of the Nodosariidae. During the mid-Pleistocene Climate Transition (1·2–0·6 Ma) in the Southern Ocean, these extinct taxa exhibited three pulses of glacial decline in abundance and diversity separated by partial interglacial recoveries. Beneath the high-productivity Benguela Current upwelling region (Sites 1082, 1083), glacial declines in the extinct taxa were suppressed by favourable high organic-carbon flux and consequent low-oxygen bottom conditions. Here two major pulses of diversity loss occurred at c.  1·3–1·2 Ma and 1·0–0·7 Ma. At all three locations, the most dramatic decline in abundance and diversity occurred c.  0·85–0·80 Ma (marine isotope stage 20), and the final disappearance of Extinction Group taxa was completed by 0·67 Ma beneath the Benguela Current and 0·60 Ma in the Southern Ocean. We speculate that this period of enhanced global extinctions was linked to a pulsed decline in glacial temperatures and/or increase in ventilation of deep and intermediate water masses, associated with polar ice cap growth since the late Pliocene.     

Molecular phylogeny of glacial relict species: a case of freshwater Valvatidae molluscs (Mollusca: Gastropoda) in North and East Asia

The study of glacial relict species has been focused on understanding how the biogeographic patterns of species have developed. A number of studies using phylogenetic and population genetics approaches have been conducted for terrestrial glacial relict species, and the mechanisms of their formation have been elucidated. On the other hand, less focus has been placed on glacial relict species inhabiting freshwater systems. In particular, stable lakes can serve as refugia during a glacial period, but research studies on freshwater relict species inhabiting lakes have not been well conducted. In order to clarify the mechanism of the glacial relict species in freshwater, we conducted a molecular phylogeny analysis, divergence time estimation, and a biogeographic reconstruction on freshwater Valvatidae molluscs, which have been considered as a glacial relict in the Japanese Archipelago. Our study shows that the valvatid fauna in the Japanese Archipelago was produced by multiple dispersal events from the Asian continent and by vicariance events during the period of the Pliocene–Quaternary glaciation. It includes multiple relict species that survived interglacial periods in different lakes. These findings suggest that the lakes can serve as refugia not only during glacial periods, but also during interglacial periods.     

Late Pliocene and Quaternary Eurasian locust infestations in the Canary Archipelago

Meco, J., Muhs, D.R., Fontugne, M., Ramos, A.J.G., Lomoschitz, A. & Patterson, D. 2010: Late Pliocene and Quaternary Eurasian locust infestations in the Canary Archipelago. Lethaia, Vol. 44, pp. 440–454. The Canary Archipelago has long been a sensitive location to record climate changes of the past. Interbedded with its basalt lavas are marine deposits from the principal Pleistocene interglacials, as well as aeolian sands with intercalated palaeosols. The palaeosols contain African dust and innumerable relict egg pods of a temperate‐region locust (cf. Dociostaurus maroccanus Thunberg 1815 ). New ecological and stratigraphical information reveals the geological history of locust plagues (or infestations) and their palaeoclimatic significance. Here, we show that the first arrival of the plagues to the Canary Islands from Africa took place near the end of the Pliocene, ca. 3 Ma, and reappeared with immense strength during the middle Late Pleistocene preceding MIS (marine isotope stage) 11 (ca. 420 ka), MIS 5.5 (ca. 125 ka) and probably during other warm interglacials of the late Middle Pleistocene and the Late Pleistocene. During the Early Holocene, locust plagues may have coincided with a brief cool period in the current interglacial. Climatically, locust plagues on the Canaries are a link in the chain of full‐glacial arid–cold climate (calcareous dunes), early interglacial arid–sub‐humid climate (African dust inputs and locust plagues), peak interglacial warm–humid climate (marine deposits with Senegalese fauna), transitional arid–temperate climate (pedogenic calcretes), and again full‐glacial arid–cold climate (calcareous dunes) oscillations. During the principal interglacials of the Pleistocene, the Canary Islands recorded the migrations of warm Senegalese marine faunas to the north, crossing latitudes in the Euro‐African Atlantic. However, this northward marine faunal migration was preceded in the terrestrial realm by interglacial infestations of locusts. □Locust plagues, Canary Islands, Late Pliocene, Pleistocene, Holocene, palaeoclimatology.