Latitudinal Temperature Gradient Research Articles

Increase in marine provinciality over the last 250 million years governed more by climate change than plate tectonics.

Amidst long-term fluctuations of the abiotic environment, the degree to which life organizes into distinct biogeographic provinces (provinciality) can reveal the fundamental drivers of global biodiversity. Our understanding of present-day biogeography implies that changes in the distribution of continents across climatic zones have predictable effects on habitat distribution, dispersal barriers and the evolution of provinciality. To assess marine provinciality through the Phanerozoic, here we (a) simulate provinces based on palaeogeographic reconstructions and global climate models and (b) contrast them with empirically derived provinces that we define using network analysis of fossil occurrences. Simulated and empirical patterns match reasonably well and consistently suggest a greater than 15% increase in provinciality since the Mesozoic era. Although both factors played a role, the simulations imply that the effect of the latitudinal temperature gradient has been twice as important in determining marine provinciality as continental configuration.

Novel species interactions and environmental conditions reduce foraging competency at the temperate range edge of a range-extending coral reef fish

Poleward range extensions of coral reef species can reshuffle temperate communities by generating competitive interactions that did not exist previously. However, novel environmental conditions and locally adapted native temperate species may slow tropical invasions by reducing the ability of invaders to access local resources (e.g. food and shelter). We test this hypothesis on wild marine fish in a climate warming hotspot using a field experiment encompassing artificial prey release. We evaluated seven behaviours associated with foraging and aggressive interactions in a common range-extending coral reef fish (Abudefduf vaigiensis) and a co-shoaling temperate fish (Microcanthus strigatus) along a latitudinal temperature gradient (730 km) in SE Australia. We found that the coral reef fish had reduced foraging performance (i.e. slower prey perception, slower prey inspection, decreased prey intake, increased distance to prey) in their novel temperate range than in their subtropical range. Furthermore, higher abundance of temperate fishes was associated with increased retreat behaviour by coral reef fish (i.e. withdrawal from foraging on released prey), independent of latitude. Where their ranges overlapped, temperate fish showed higher foraging and aggression than coral reef fish. Our findings suggest that lower foraging performance of tropical fish at their leading range edge is driven by the combined effect of environmental factors (e.g. lower seawater temperature and/or unfamiliarity with novel conditions in their extended temperate ranges) and biological factors (e.g. increased abundance and larger body sizes of local temperate fishes). Whilst a future increase in ocean warming is expected to alleviate current foraging limitations in coral reef fishes at leading range edges, under current warming native temperate fishes at their trailing edges appear able to slow the range extension of coral reef fishes into temperate ecosystems by limiting their access to resources.

Cold water temperatures define the poleward range limits of south American fiddler crabs

Temperature increase due to climate change has caused shifts in the range distribution of several organisms globally. In coastal intertidal environments most organisms have an amphibious life cycle and their poleward range limits may be delimited by their thermal tolerance during the pelagic larval stages. Fiddler crabs are key species in intertidal environments and their early larval stages occur in coastal waters. We evaluated the mean and monthly minimum sea surface temperature (SST) gradient over the South American coast and compared it to the minimum and maximum critical thermal limits (CTmin and CTmax) of the first larval stage of eight fiddler crab species to assess whether temperature delimits their distributional ranges. We found a clinal decrease in mean SST of 0.28 °C per latitudinal degree along the distribution of fiddler crabs in South America. Cold tolerance differed among the larvae of fiddler crab species, which corresponds to the latitudinal temperature gradient observed in their poleward range limits. Thus, our results suggest that cold water temperature can define the poleward range limits of South American fiddler crabs. The CTmax cannot explain the northern poleward range limits of the fiddler crabs. Fiddler crabs larvae showed a similar tolerance to high temperatures (mean 40.5 °C) regardless of species (except Leptuca uruguayensis) and these are higher than environmental temperatures observed in South America. We also observed an increase in mean SST of 0.9 °C in the last 37 years. This increase in water temperature may explain the recent poleward range expansion of one South American fiddler crab species, Leptuca cumulanta. Therefore, we showed that differential thermal responses at the early larval stage have consequences on the geographic range limits of the fiddler crab species. Our findings allow us to hypothesize that fiddler crabs’ poleward range limits may expand to higher latitudes in the future due to global warming.

Transcriptomic signatures of temperature adaptation in the eastern oyster Crassostrea virginica.

The large geographic distribution of the eastern oyster, Crassostrea virginica, makes it an ideal species to test how populations have adapted to latitudinal gradients in temperature. Despite inhabiting distinct thermal regimes, populations of C. virginica near the species' southern and northern geographic range show no population differences in their physiological response to temperature. In this study, we used comparative transcriptomics to understand how oysters from either end of the species' range maintain enantiostasis across three acclimation temperatures (10, 20, and 30°C). With this approach, we identified genes that were differentially expressed in response to temperature between individuals of C. virginica collected from New Brunswick, Canada and Louisiana, USA. We observed a core set of genes whose expression responded to temperature in both populations, but also an even larger set of genes with expression patterns that were unique to each population. Intriguingly, the genes with population-specific responses to temperature had elevated FST and Ka/Ks ratios compared to the genome-wide average. In contrast, genes showing only a response to temperature were found to only have elevated FST values suggesting that divergent FST may be due to selection on linked regulatory regions rather than positive selection on protein coding regions. Taken together, our results suggest that, despite coarse-scale physiological similarities, natural selection has shaped divergent gene expression responses to temperature in geographically separated populations of this broadly eurythermal marine invertebrate.

Effects of Autumn Warming on Energy Consumption of Diapausing Fall Webworm (Lepidoptera: Arctiidae) Pupae.

Since its invasion into China in 1979, the fall webworm, Hyphantria cunea Drury, has spread from Dandong city (about 40°N) in Liaoning Province to Nanjing city (about 32°N) in Jiangsu Province, and to other areas. Owing to geographic and latitudinal gradients in temperature, H. cunea will encounter temperature changes during the spreading process. In this study, we verified the hypothesis that autumn warming accelerates the energy consumption of H. cunea diapause pupae. We found that, after autumn warming, the body size and mass of diapause pupae decreased significantly and raised constant temperature accelerated carbohydrate and protein consumption in female pupae, while fluctuating temperature changes had a more pronounced effect on carbohydrate and protein consumption in male pupae. Contrary to expectations, the lipid content of diapause pupae did not decrease after autumn warming, and even increased significantly. We conclude that warming in autumn accelerates energy consumption by diapause pupae, and the autumn energy consumption of diapause pupae is dominated by carbohydrates, supplemented by protein when carbohydrates are overconsumed, while lipid use is dominated by anabolic metabolism during autumn.

An extreme climate gradient-induced ecological regionalization in the Upper Cretaceous Western Interior Basin of North America

Abstract The Upper Cretaceous Western Interior Basin of North America provides a unique laboratory for constraining the effects of spatial climate patterns on the macroevolution and spatiotemporal distribution of biological communities across geologic timescales. Previous studies suggested that Western Interior Basin terrestrial ecosystems were divided into distinct southern and northern communities, and that this provincialism was maintained by a putative climate barrier at ∼50°N paleolatitude; however, this climate barrier hypothesis has yet to be tested. We present mean annual temperature (MAT) spatial interpolations for the Western Interior Basin that confirm the presence of a distinct terrestrial climate barrier in the form of a MAT transition zone between 48°N and 58°N paleolatitude during the final 15 m.y. of the Cretaceous. This transition zone was characterized by steep latitudinal temperature gradients and divided the Western Interior Basin into warm southern and cool northern biomes. Similarity analyses of new compilations of fossil pollen and leaf records from the Western Interior Basin suggest that the biogeographical distribution of primary producers in the Western Interior Basin was heavily influenced by the presence of this temperature transition zone, which in turn may have impacted the distribution of the entire trophic system across western North America.

Biogeography and phenology of the jellyfish Rhizostoma pulmo (Cnidaria: Scyphozoa) in southern European seas

AbstractAimGlobal anthropogenic changes have altered biogeography and phenology of marine populations, thereby promoting a spatial reconfiguration in the functioning of marine ecosystems. Among these changes, massive proliferations of jellyfish in temperate latitudes warn of potential alterations in biogeochemical fluxes, ecosystems’ structure and assets, and the services they provide to human welfare. Understanding driving factors shaping large‐scale patterns of jellyfish proliferations is a pressing need in global ecology and sustainability science. Using a comprehensive dataset of the largest blooming scyphomedusae in southern European seas we test, over broad space–time scales, current hypotheses relating jellyfish dynamics to warming and eutrophication.LocationSouthern European seas.Time period1875–2019.Major taxa studiedRhizostoma pulmo.MethodsWe have gathered historical and contemporaneous records of R. pulmo from the Mediterranean and Black Seas over the last two centuries (7,359 records). Generalized statistical models were used to assess the influence of thermal (latitudinal) and productivity (longitudinal) gradients on the biogeographical patterns, and the species’ phenology at large and regional scales.ResultsRhizostoma pulmo abundance exhibited an enhanced magnitude and frequency in recent decades, concurrently with positive temperature anomalies. We found that the latitudinal temperature gradient, but not productivity, shaped long‐term bloom intensity and biogeographical patterns of the species. Our analysis further uncovered a significant effect of the interannual variability of spring temperature on the species’ phenology over the period 2008–2018, with warmer springs favouring an earlier start (c. 3 months) and a longer duration (from 5 to 7 months) of jellyfish season.Main conclusionsAmong the current hypotheses linking jellyfish changes with anthropogenic disturbances, only the warming‐based hypothesis gained support over wide space–time scales, while the eutrophication‐based hypothesis mainly applied at local scales. Hence, biogeographical patterns of R. pulmo are shaped by the latitudinal temperature gradient, while the species bloom dynamics echo variations in ecoregion thermal regimes.

Dropstones in the Mar del Plata Canyon Area (SW Atlantic): Evidence for Provenance, Transport, Distribution, and Oceanographic Implications

AbstractA variety of gravel‐ to cobble‐sized rocks, recovered from the Mar del Plata (MdP) Canyon area (Western South Atlantic at 38°S) and interpreted as ice‐rafted debris, represent the first evidence that large icebergs have floated in the Falkland (Malvinas) Current from the southern polar high latitudes far northward. Detailed petrographic analyses identified the Antarctic Peninsula, sub‐Antarctic islands in the Scotia Sea, and Tierra del Fuego as plausible source areas. The drift process could have started as early as at the beginning of the last deglaciation, according to an age obtained from a cold‐water coral fragment associated with one of the dropstones. At the end of the Last Glacial Maximum, large icebergs have been supplied to the Antarctic Circumpolar Current, captured by those ocean current branches that circumvent the Falkland (Malvinas) Islands and entered the Argentine Margin. When the iceberg fleets approached the Brazil‐Falkland (Malvinas) Confluence Zone with its steep latitudinal temperature gradient, the icebergs got oceanographically trapped and melted off rapidly. The sediment load sinking down to the seafloor formed a dropstone blanket particularly where the MdP Canyon had incised into the continental slope. Here, mass‐flow processes, induced by local slope instability, and along‐slope sediment resorting, due to the erosional effects of strong and persistent contouritic bottom currents, favored local enrichment in dropstones in the form of a loose, coarse sediment drape inside morphological depressions. The bottom current velocity would be locally strong enough to rework this sediment, leaving coarse rafted debris as a lag deposit.

Southward migration of the Southern Hemisphere westerly winds corresponds with warming climate over centennial timescales

Recent changes in the strength and location of the Southern Hemisphere westerly winds (SHW) have been linked to continental droughts and wildfires, changes in the Southern Ocean carbon sink, sea ice extent, ocean circulation, and ice shelf stability. Despite their critical role, our ability to predict their impacts under future climates is limited by a lack of data on SHW behaviour over centennial timescales. Here, we present a 700-year record of changes in SHW intensity from sub-Antarctic Marion Island using diatom and geochemical proxies and compare it with paleoclimate records and recent instrumental data. During cool periods, such as the Little Ice Age (c. 1400–1870 CE), the winds weakened and shifted towards the equator, and during warm periods they intensified and migrated poleward. These results imply that changes in the latitudinal temperature gradient drive century-scale SHW migrations, and that intensification of impacts can be anticipated in the coming century.

Inter-hemispheric synchroneity of Holocene precipitation anomalies controlled by Earth\u2019s latitudinal insolation gradients

Atmospheric circulation is a fundamental component of Earth’s climate system, transporting energy poleward to partially offset the latitudinal imbalance in insolation. Changes in the latitudinal distribution of insolation thus force variations in atmospheric circulation, in turn altering regional hydroclimates. Here we demonstrate that regional hydroclimates controlled by the Northern Hemisphere mid-latitude storm tracks and the African and South American Monsoons changed synchronously during the last 10 kyrs. We argue that these regional hydroclimate variations are connected and reflect the adjustment of the atmospheric poleward energy transport to the evolving differential heating of the Northern and Southern Hemispheres. These results indicate that changes in latitudinal insolation gradients and associated variations in latitudinal temperature gradients exert important control on atmospheric circulation and regional hydroclimates. Since the current episode of global warming strongly affects latitudinal temperature gradients through Arctic amplification, our results can inform projections of likely inter-hemispheric precipitation changes in the future.

What drove the evolutionary trend of planktic foraminifers during the Cretaceous: Oceanic Anoxic Events (OAEs) directly affected it?

Abstract The oceanic redox state has played an essential role in the evolution of life on earth, and oceanic “anoxic events” have been proposed as one of the causal mechanisms for mass extinctions. During the mid-Cretaceous, oceanic anoxic events (OAEs) occurred several times and had a substantial impact on the biosphere. Planktic foraminifers are marine planktons with calcite tests, and their shells constitute approximately 30%–80% of modern deep-marine calcite; thus, they play a key role in the global carbon cycle. Previous studies have reported that at, or near, the times of major Cretaceous OAEs, planktic foraminifers have a high turnover (extinction and speciation) rate. However, the precise impact of anoxic conditions on the evolutionary trend of planktic foraminifers remained obscure. In this study, we investigate this by assessing the extinction/speciation rate of planktic foraminifers around OAEs. Our results suggest that the development of anoxia during OAEs would not have had a direct effect on the evolutionary trend (i.e., species number and turnover ratio). Two foraminiferal turnovers occurred around OAE1a and OAE2, however, all five turnover peaks seem to be largely associated with a relatively short-term (0.5–3 Myr) eustatic curve. Decreasing species numbers of planktic foraminifers are associated with a relatively lower sea eustatic level (second-order; ~20 Myr) and a small latitudinal temperature gradient around OAE1b, which are not anoxic conditions. Changes in oceanographical parameters (i.e., surface biological productivity, water column structure, carbonate chemistry, and nutrients) related to lowering sea-levels might have had a significant effect on foraminiferal evolutionary trends.

The vertical profile of recent tropical temperature trends: Persistent model biases in the context of internal variability

Tropospheric and stratospheric tropical temperature trends in recent decades have been notoriously hard to simulate using climate models, particularly in the upper troposphere. Aside from the warming trend itself, this has broader implications, e.g. atmospheric circulation trends depend on latitudinal temperature gradients. In this study, tropical temperature trends in the CMIP6 models are examined, from 1979 to 2014, and contrasted with trends from the RICH/RAOBCORE radiosondes, and the ERA5/5.1 reanalysis. As in earlier studies, we find considerable warming biases in the CMIP6 modeled trends, and we show that these biases are linked to biases in surface temperature. We also uncover previously undocumented biases in the lower-middle stratosphere: the CMIP6 models appear unable to capture the time evolution of stratospheric cooling, which is non-monotonic owing to the Montreal Protocol. Finally, using models with large ensembles, we show that their standard deviation in tropospheric temperature trends, which is due to internal variability alone, explains ∼ 50% (± 20%) of that from the CMIP6 models.

Impact of nutrients and water level changes on submerged macrophytes along a temperature gradient: A pan-European mesocosm experiment.

Submerged macrophytes are of key importance for the structure and functioning of shallow lakes and can be decisive for maintaining them in a clear water state. The ongoing climate change affects the macrophytes through changes in temperature and precipitation, causing variations in nutrient load, water level and light availability. To investigate how these factors jointly determine macrophyte dominance and growth, we conducted a highly standardized pan-European experiment involving the installation of mesocosms in lakes. The experimental design consisted of mesotrophic and eutrophic nutrient conditions at 1m (shallow) and 2m (deep) depth along a latitudinal temperature gradient with average water temperatures ranging from 14.9 to 23.9°C (Sweden to Greece) and a natural drop in water levels in the warmest countries (Greece and Turkey). We determined percent plant volume inhabited (PVI) of submerged macrophytes on a monthly basis for 5months and dry weight at the end of the experiment. Over the temperature gradient, PVI was highest in the shallow mesotrophic mesocosms followed by intermediate levels in the shallow eutrophic and deep mesotrophic mesocosms, and lowest levels in the deep eutrophic mesocosms. We identified three pathways along which water temperature likely affected PVI, exhibiting (a) a direct positive effect if light was not limiting; (b) an indirect positive effect due to an evaporation-driven water level reduction, causing a nonlinear increase in mean available light; and (c) an indirect negative effect through algal growth and, thus, high light attenuation under eutrophic conditions. We conclude that high temperatures combined with a temperature-mediated water level decrease can counterbalance the negative effects of eutrophic conditions on macrophytes by enhancing the light availability. While a water level reduction can promote macrophyte dominance, an extreme reduction will likely decrease macrophyte biomass and, consequently, their capacity to function as a carbon store and food source.

Modeling climate-vegetation interactions during the last interglacial: The impact of biogeophysical feedbacks in North Africa

Previous climate model simulations of the early Last Interglacial (LIG) underestimated the temperatures compared to proxy-based reconstructions. One possible reason for this underestimation is that in these simulations the vegetation was prescribed to a pre-industrial state. To study the impact of climate-vegetation interactions, we performed a series of model experiments using the iLOVECLIM climate model, in which either VECODE or LPJ-GUESS was coupled as vegetation component. We specifically assessed the evolution of vegetation during the LIG and the magnitude of dynamical vegetation feedbacks. Our results show a relatively high vegetation cover (>70%) in the Sahara during the early LIG when the summer insolation at 20°N was high. This early stage is followed by an accelerated desertification phase after 123 ka BP. The rates of desertification in the Sahara peak at 122 ka BP, responding to the fast decline in 20°N July insolation. This desertification is accelerated when the magnitude of positive vegetation feedbacks on precipitation cannot offset the moisture deficit due to decreased summer insolation.Simulations including the LIG vegetation feedback suggest warmer conditions than simulations with prescribed pre-industrial vegetation, but they still slightly underestimate the temperature suggested by proxy records. This is particularly the case in the high latitude regions and the tropics, where the 125 ka BP vegetation cover is significantly higher than the pre-industrial state. The magnitude of vegetation feedbacks in North Africa to local climate peaks in the early LIG and decreases during the LIG, corresponding to temporal vegetation changes. During the early LIG, experiments with dynamical vegetation suggested a doubling in the amount of precipitation (∼60 cm/yr) in comparison to experiments with fixed pre-industrial vegetation. In addition, adding dynamical vegetation causes higher surface temperatures by about 2.5 °C in North Africa. At a global scale, a vegetated Sahara during the early LIG leads to an increase in surface temperature and a decline in surface air pressure due to local feedbacks, thereby enhancing mid-latitude westerlies as a result of increased latitudinal temperature and pressure gradient, leading to an increase in the amount of heat transported by the atmosphere from tropical regions to the Arctic. This green Sahara feedback provides 30% of the total contribution of global vegetation feedbacks to high latitudes warming.

Potential feminization of Red Sea turtle hatchlings as indicated by in situ sand temperature profiles

AbstractClimate change poses a serious threat to species that demonstrate temperature‐dependent sex determination, including marine turtles. Increased temperatures can result in highly female‐skewed sex ratios and decreased hatching success. The pivotal temperature that delineates hatchling sex ratios is commonly considered to be 29.2°C, but whether this threshold applies to turtles in the Red Sea region has not been tested in situ. For all species of marine turtles, there is a supposed thermal range of 25–33°C in which egg incubation is successful, with prolonged temperatures above 33°C resulting in morphological abnormalities and hatchling mortality. Sand temperature data were collected from May–September 2018 from the average nesting depth of hawksbill (Eretmochelys imbricata) and green turtles (Chelonia mydas) at five study sites. We calculated the expected sex ratio based on a maximum likelihood model. The sand temperature profile at four of the sites exceeded the pivotal temperature (29.2°C) throughout the study duration, which suggests feminization of turtles could be occurring; however, the pivotal temperature in this region still needs to be empirically confirmed. The percentage of days with sand temperature exceeding the maximum thermal threshold between June 3, and September 16, 2018, was site‐specific rather than determined by latitudinal temperature gradients, and ranged between 0 and 100% of days. Maximum temperature recordings were as high as 36.0 and 35.3°C at 30 and 50 cm depth, respectively. Nesting sites in the Red Sea region could already be exceeding the thermal limits and may be particularly vulnerable to rising temperatures. Sites with lower sand temperatures, such as Small Gobal Island, may represent priority areas for conservation efforts. Alternatively, local adaptation may be a reality under extremely warm conditions, thus, further research into the thermal tolerance of hatchlings in the region could provide insight on how they might adapt to future climate change.

Does Sea Surface Temperature Affect Solubility of Iron in Mineral Dust? The Gulf of California as a Case Study

AbstractEolian transport of mineral dust is one of the main inputs of iron (Fe) to the global ocean; however, the magnitude and biogeochemical impact of this supply depends on the solubility of the deposited dust. In particular, the effect of temperature on Fe‐bearing dust solubility has been scarcely investigated even though a seasonal gradient of sea surface temperature (SST) is a common feature in coastal zones adjacent to the major dust source regions of the world. In this work, the effect of temperature on the fractional solubility of Fe (FFeS) was evaluated experimentally using sieved soils (as a dust proxy) from the Baja California Peninsula and surface seawater from the Gulf of California (GC). Two incubations were performed at 17°C (winter) and 29°C (summer) considering the seasonal variability of SST in the GC. Differences in FFeS up to 3 orders of magnitude (0.003–4.49%) were linked to incubation temperature, dust load, and contact time between seawater and dust. After 72 hr of incubation, the effect of temperature was statistically significant (p < 0.05) for all dust treatments, with FFeS higher (4–24 times) at 29°C. High FFeS in warmer waters are a result of increased Fe‐bearing dust dissolution and decreased scavenging of Fe by dust particles. Since temperature appears to control the magnitude of FFeS in the GC, we suggest that this factor could have an effect on the atmospheric inputs of soluble Fe in marginal seas with similar seasonal SST contrasts; including the global ocean, where well‐defined latitudinal temperature gradients exist.

Stress in the tropics? Impact of a latitudinal seawater δ18O gradient on Middle Jurassic temperature reconstructions at low latitudes

Abstract Previous stable oxygen isotope records of calcitic fossils (δ18Oshell) from Europe have been interpreted to reflect strong climatic perturbations throughout the Jurassic, but it is unknown whether they reflect global trends because data from other regions are sparse. Here, we use bivalve and brachiopod shells from western Asia and northern Africa to examine seawater temperatures at low latitudes as well as latitudinal temperature gradients in the Middle Jurassic. Our results include the first absolute temperature estimates for most of the study areas and this time interval. Furthermore, we acknowledge a latitudinal gradient in δ18O values of seawater (δ18Osea) that leads to more realistic temperature reconstructions of tropical water temperatures, which were underestimated by earlier methods. Following this approach, δ18Oshell values translate into average equatorial water temperatures during the Middle Jurassic several degrees higher than today (as high as 34–35 °C). Such high temperatures cause environmental stress, probably explaining previously documented low diversities of low-latitudinal ecosystems (e.g., coral reefs) during this time interval. A comparison with literature data raises doubts over whether previously published European temperature curves are truly representative of global patterns. Instead, they might reflect the complex paleogeography of European basins influenced by regional and/or short-term changes in δ18Osea values.

A Dynamical Framework for Interpreting Ancient Sea Surface Temperatures

AbstractEfforts to estimate past global mean temperature and latitudinal gradients must contend with spatial heterogeneity in sea surface temperatures (SSTs). Here, we use modern SSTs to show that the environments from which most paleoclimatic data are drawn, shallow epeiric seas and continental margins, are systematically offset from zonal mean temperatures. Epeiric seas are warmer and more seasonal than open‐ocean values from the same latitudes, while continental margins exhibit consistent and predictable deviations related to gyre circulation. Warm temperatures inferred from Paleozoic proxy data may largely reflect that these data derive almost entirely from epeiric seas. Moreover, pseudoproxy analysis using Paleogene sampling localities demonstrates how undersampling of the full range of dynamical environments associated with gyre circulation can generate spurious estimates of latitudinal temperature gradients. Recognition of these global patterns permits a predictive framework within which to more robustly interpret proxy data, improve Earth system models, and reconstruct ancient dynamic regimes.

Terrestrial mollusk records in the loess sequences from eastern Central Asia since the last deglaciation and their paleoenvironmental significance

A variety of proxies has been studied to document paleoclimatic changes in arid Central Asia (ACA). However, biological archives, which can be directly related to climatic conditions, are still scarce in this region. Here we report records of the total count fossils (TCF) of terrestrial mollusks, organic carbon isotopes (δ13Corg) and loss on ignition (LOI), since the last deglaciation in the Talede and XRBLK loess sections in Xinjiang, eastern Central Asia. Prior to the Holocene, the records show rare fossils with relatively low LOI and more positive δ13Corg, indicating low biomass/organic carbon content under dry conditions which were unfavorable for the survival of snails. In contrast, TCF increased abruptly at the beginning of Holocene, coincident with a prominent increase in LOI and a marked negative shift in δ13Corg. Furthermore, TCF increased gradually to its maximum and δ13Corg became progressively negative with constant high LOI from the early to late Holocene. The variations imply a trend towards wetter environment, with optimal moisture (precipitation/relative humidity) conditions occurring in the late Holocene. Overall, this Holocene moisture evolution history could be attributed to the variations of Westerlies strength modulated by the latitudinal temperature gradient and the insolation-related evaporation should also be concerned.

Reconstructing Arctic Precipitation Seasonality Using Aquatic Leaf Wax δ2H in Lakes With Contrasting Residence Times

AbstractArctic precipitation is predicted to increase this century. Records of past precipitation seasonality provide baselines for a mechanistic understanding of the dynamics controlling Arctic precipitation. We present an approach to reconstruct Arctic precipitation seasonality using stable hydrogen isotopes (δ2H) of aquatic plant waxes in neighboring lakes with contrasting water residence times and present a case study of this approach in two lakes on western Greenland. Residence time calculations suggest that growing season lake water δ2H in one lake reflects summer precipitation δ2H, while the other reflects amount‐weighted annual precipitation δ2H and evaporative enrichment. Aquatic plant wax δ2H in the “summer lake” is relatively constant throughout the Holocene, perhaps reflecting competing effects of local summer warmth and increased distal moisture transport due to a strengthened latitudinal temperature gradient. In contrast, aquatic plant wax δ2H in the “mean annual lake” is 100‰ 2H depleted from 6 to 4 ka relative to the beginning and end of the record. Because there are relatively minor changes in summer precipitation δ2H, we interpret the 100‰ 2H depletion in mean annual precipitation to reflect an increase in winter precipitation amount, likely accompanied by changes in winter precipitation δ2H and decreased evaporative enrichment. Thus, unlike the “summer lake,” the “mean annual lake” records changes in winter precipitation. This dual‐lake approach may be applied to reconstruct past changes in precipitation seasonality at sites with strong precipitation isotope seasonality and minimal lake water evaporative enrichment.