Paleoclimate Archives Research Articles

Nouveautés sur les tumeurs épithélioïdes des tissus mous

Long and continuous terrestrial paleoclimate records are important in understanding forcing mechanisms of Cenozoic climate. However, such records are rare. Sediments in basins near the edges of the Tibetan Plateau are potential paleoclimate archives, but dating them is a challenge. Here we report a successful application of paleomagnetism to a set of fluvio-lacustrine sediments in the Tianshui Basin, NE Tibet, and found that this set of sediments spans ∼17.1–6.1 Ma. Preliminary biomarker studies found that this set of sediments has climatically important organic components and, thus, these sediments are perfect paleoclimatic archives. Generating high-resolution biomarker records will be able to cast light on climatic history in NE Tibet during the Miocene.

Paleomagnetic ages of Miocene fluvio-lacustrine sediments in the Tianshui Basin, western China

Long and continuous terrestrial paleoclimate records are important in understanding forcing mechanisms of Cenozoic climate. However, such records are rare. Sediments in basins near the edges of the Tibetan Plateau are potential paleoclimate archives, but dating them is a challenge. Here we report a successful application of paleomagnetism to a set of fluvio-lacustrine sediments in the Tianshui Basin, NE Tibet, and found that this set of sediments spans ∼17.1–6.1Ma. Preliminary biomarker studies found that this set of sediments has climatically important organic components and, thus, these sediments are perfect paleoclimatic archives. Generating high-resolution biomarker records will be able to cast light on climatic history in NE Tibet during the Miocene.

Tree-ring derived Little Ice Age temperature trends from the central British Columbia Coast Mountains, Canada

Most glaciers in the British Columbia Coast Mountains reached their maximum Holocene extent during the Little Ice Age. Early- and late-Little Ice Age intervals of expansion and retreat fluctuations describe a mass-balance response to changing climates. Although existing dendroclimatic records provide insights into these climatic fluctuations over the last 400yr, their short durations prohibit evaluation of early-Little Ice Age climate variability. To extend the duration of these records, submerged coarse woody debris salvaged from a high-elevation lake was cross-dated to living chronologies. The resulting chronology provides the opportunity to reconstruct a regional June–July air-temperature anomaly record extending from AD1225 to 2010. The reconstruction shows that the intervals AD1350–1420, 1475–1550, 1625–1700 and 1830–1940 characterized distinct periods of below-average June–July temperature followed by periods of above-average temperature. Our reconstruction provides the first annually resolved insights into high-elevation climates spanning the Little Ice Age in this region and indicates that Little Ice Age moraine stabilization corresponds to persistent intervals of warmer-than-average temperatures. We conclude that coarse woody debris submerged in high-elevation lakes has considerable potential for developing lengthy proxy climate records, and we recommend that researchers focus attention on this largely ignored paleoclimatic archive.

Aridity and vegetation composition are important determinants of leaf-wax δD values in southeastern Mexico and Central America

Leaf-wax hydrogen isotope composition (δDwax) is increasingly applied as a proxy for hydroclimate variability in tropical paleoclimate archives, but the factors controlling δDwax in the tropics remain poorly understood. We measured δDwax and the stable carbon isotope composition of leaf-waxes (δ13Cwax), including both n-alkanes and n-alkanoic acids, from modern lake sediments and soils across a marked aridity gradient in southeastern Mexico and northern Central America to investigate the importance of aridity and vegetation composition on δDwax. In this region the estimated hydrogen isotope composition of meteoric water (δDw) varies by only 25‰, and variability in δDw does not explain the relatively large variance in δDwax (60‰). Instead, the aridity index, defined as the ratio of mean annual precipitation to mean annual potential evapotranspiration (MAP/PET), explains much of the variability in the hydrogen isotope fractionation between leaf-waxes and meteoric water (εwax/w). Aridity effects are more evident in lake sediments than in soils, possibly because integration of leaf-waxes across a broad catchment masks small-scale variability in εwax/w that is a consequence of differences in vegetation and microclimates. In angiosperm-dominated environments, plant ecology, inferred from δ13Cwax, provides a secondary control on εwax/w for n-alkanoic acids (εn-acid/w). Low δ13Cn-acid values are associated with high εn-acid/w values, most likely reflecting differences in biosynthetic hydrogen isotope fractionation between C4 grasses and C3 trees and shrubs. A similar relationship between δ13Cn-alkane and εn-alkane/w is not observed. These results indicate that changes in either aridity or vegetation can cause large variability in δDwax that is independent of the isotopic composition of precipitation, and these effects should be accounted for in paleoclimate studies.

Groundwater residence time and paleorecharge conditions in the deep confined aquifers of the coastal watershed, South-East Tanzania

Summary Analysis of radiocarbon and stable isotopes of C, H and O in groundwater samples from the coastal watershed of Southeastern Tanzania is used to decipher the age of groundwater and the climatic conditions at the time of recharge. Radiocarbon dating was corrected on the basis of stable carbon isotope ratios and hydrochemical data. Two main recharge periods are recognised: (1) a recent recharge period with residence times dated to younger than 1.3 ka BP, for the shallow aquifer and some deep groundwater aquifers; and (2) a paleorecharge occurring during the Late Pleistocene to Holocene transition (between 6 and 13 ka BP), for the lower confined aquifer. The climatic excursions (arid and humid phases) identified in this study match well with those identified from studies of paleo-climatic records in Tanzania and East Africa. The oxygen-18 and radiocarbon results show that there is a potential mixing of groundwater of varying ages along flow paths in the coastal aquifer system. This has also been shown by redox parameters in some of the deeper aquifer samples. The data also revealed that there is relatively simple pattern of lateral groundwater flow in the deeper confined aquifer. Isotopic evidence from this study and related studies in paleolimnology improves our knowledge of the past climates. The data suggests that the paleorecharge to the confined aquifer was from inland under wetter climatic conditions than present. Therefore, paleorecharge from the adjacent mountain regions to coastal area like Ifakara, Morogoro and Udzungwa mountains could be important parts of recharge area of the Kimbiji aquifer. However, the hinterland mountains of Dar es Salaam (mainly Pugu, Mkuranga, Ruvu and Kisarawe) could also play an important role in replenishing the Kimbiji coastal aquifers. In contrast, recharge in the shallow unconfined aquifer is characterized by local rainfall and river water infiltration. This study is the first of its kind, assessing fingerprinting of paleoclimates in Southeastern coastal Tanzania using the isotopic composition of deep groundwater aquifers. The freshwater resources in the Neogene aquifer contain paleo-groundwater aquifers that have been mixed with recently-recharged flow systems. Hence, the resources may be sustainable. This study also provides information that may be useful for designing optimum strategies for a sustainable management of groundwater resources in the coastal aquifer, and it testifies to the importance of groundwater as a paleoclimatic archive. Such information is also essential for consideration by modellers in their attempts to simulate the hydrogeological processes in confined aquifers over very long time spans.

U-series dating of the travertine depositing near the Rongma hot springs in northern Tibet, China, and its paleoclimatic implication

High resolution age data obtained by travertine dating is necessary for the reconstruction of paleoclimate and palaeohydrology near Rongma hot springs in northern Tibet. U-series dating of a travertine cone depositing in the study area was used. The results show that the U contents of the travertine samples range from 0.298 to 1.363 ppm, and the 234U/238U is in the rage of 1.475–1.700, indicating that the deposition of travertine near the Rongma hot springs is stable and continuous. The age of the travertine samples ranges from 11,500 to 4600 a, corresponding to the first stage of MIS 1. Combination of the first stage of MIS with the effect of monsoon climate of the Indian Ocean in the same period implies a warm and humid climate during the deposition of the travertines in the study area. The U-series age range in the Rongma hot springs area is coincident with that of the travertine in southern Tibet. The age data detected from travertine cone help in understanding the evolution of hydrogeology of the hot spring area. High resolution age data must be acquired before travertine can be confidently used as a paleoclimatic archive.

Deuterium and oxygen 18 in precipitation and atmospheric moisture in the upper Urumqi River Basin, eastern Tianshan Mountains

The contribution of stable isotopes in meteorological, climatological and hydrological research is well known. This study analyzed the deuterium and oxygen 18 contents (δD and δ18O) of precipitation in event-based samples at three stations (Glacier No. 1, Zongkong, Houxia) along the upper Urumqi River Basin from May 2006 to August 2007. The δ18O in precipitation revealed a wide range and a distinct seasonal variation at all three stations, with enriched values occurring in summer and depleted values in winter. A statistically significant positive correlation was observed between the δ18O and δD and local surface air temperature, and better linear relationship existed between δ18O and air temperature than that of δD. This suggests that paleoclimatic archives relating to precipitation δ18O and δD can be useful for qualitative temperature reconstruction. The d-excess in precipitation also exhibited a seasonal variability. Based on NCEP/NCAR reanalysis data, three-dimensional isentropic back-trajectories in HYSPLIT model were employed to determine the moisture source for each precipitation event. Results indicate a dominant effect of westerly air masses in summer and the integrated influence of westerly and polar air masses in winter, and d-excess can be used as a sensitive tracer of the moisture transport history.

The influence of 14C reservoir age on interpretation of paleolimnological records from the Tibetan Plateau

There is a great deal of controversy regarding the fate of glaciers and ice fields on the Tibetan Plateau in the face of continued anthropogenic global warming. Paleoclimate reconstructions and spatial analyses aimed at mapping past climate changes are the key to understanding the climatic response of the Tibetan Plateau to changing conditions. Specifically, the numerous lakes distributed across the Tibetan Plateau can provide high-resolution (spatial and temporal) climate reconstructions to investigate past changes in the climate system. In this paper, we review the primary limitation to exploiting these valuable paleoclimate archives: errors in radiocarbon-based age models. We review the techniques that have been used to estimate 14C reservoir ages on the Tibetan Plateau and compile the published 14C reservoir ages to examine their spatial and temporal patterns and to assess the imposed chronological uncertainties. Using site-specific evaluations of Bangong Co and Lake Qinghai, we demonstrate that 14C age model uncertainties permit equally probable and contrasting interpretations of existing paleoclimate records. We also examine 14C-induced uncertainties in the spatial climatic response on the Tibetan Plateau to (1) the termination of the Last Glacial Maximum and (2) the Holocene Thermal Maximum. We conclude with recommendations for reducing uncertainties in future lake-based paleoclimate studies on the Tibetan Plateau.

Eurhomalea exalbida (Bivalvia): A reliable recorder of climate in southern South America?

Due to the lack of suitable high-resolution archives, regional and continental-scale climate dynamics of southern South America are not well understood. Shells of the long-lived, shallow-marine bivalve mollusk, Eurhomalea exalbida (Dillwyn), are likely to contain information on the past water temperatures. As yet, however, no rigorous calibration study has been presented so that growth history traits and the reliability of shell oxygen isotope-based temperature estimates remain unknown. Shell growth patterns and oxygen isotope ratios of four young specimens of E. exalbida from the Falkland Islands (Southwest Atlantic) were analyzed and cross-calibrated with environmental parameters. Results indicate that E. exalbida likely captured the full seasonal temperature amplitude in its shell. Annual growth line formation occurred between fall and early winter. The most remarkable finding, however, was that E. exalbida formed its shell with an offset of −0.48 to −1.91‰ from expected oxygen isotopic equilibrium with the ambient water. If this remained unnoticed, paleotemperature estimates would overestimate actual water temperatures by 2.1–8.3°C. With increasing ontogenetic age, the discrepancy between measured and reconstructed temperatures increases exponentially, irrespective of the seasonally varying shell growth rates. We attribute this finding to a pH increase in the extrapallial fluid during ontogeny favoring a dominance of the (isotopically lighter) carbonate ions over (isotopically heavier) bicarbonate ions. When this disequilibrium fractionation effect is taken into account, E. exalbida can serve as a high-resolution paleoclimate archive for mid to high latitudes of southern South America providing quantifiable temperature estimates, even from single fossil specimens.

Reconstructing the duration of the West African Monsoon season from growth patterns and isotopic signals of shells of Anadara senilis (Saloum Delta, Senegal)

Long-term reconstructions of the seasonality of the West African Monsoon are limited by the lack of seasonally resolved paleoclimate archives in this region. We present an application based on the growth patterns and monthly resolved δ18O profiles of Anadara senilis bivalve shells to quantitatively estimate the duration of the rainy and dry seasons in the hypersaline Saloum Delta, Senegal. Fortnightly growth patterns are used to estimate changes of the growth rate and to place the shell isotope record into a temporal context. Based on fortnightly growth patterns and sharply declining δ18O values, the duration of the rainy season was estimated. As an illustrative example, we quantitatively estimated the duration of two rainy seasons and two dry seasons that occurred about 1500years ago from a fossil shell of the Dioron Boumak archaeological site to the nearest month. This precision can be statistically improved by the analysis of a larger shell number or by higher resolution isotope sampling. Our results open the possibility of using large fossil shell accumulations in the Saloum Delta for quantitative studies of the long-term variability of the West African Monsoon seasonality.

Environmental and climatic signals from stable isotopes in Anatolian tree rings, Turkey

Dendrochronological and oxygen–carbon isotopic analysis was conducted on tree rings collected at two different elevations from three different regions in western Anatolia, Turkey. Tree rings were sampled from Anatolian black pines (Pinus nigra Arn. subsp. pallasiana (Lamb.) Holmboe) of at least 200 years old through an N–S transect covering Bolu-Mengen (north), Kutahya–Simav, and Antalya–Alanya (south) forests. Cellulose was extracted from 5-year blocks of tree rings from lower to upper altitudes in each region. Dendrochronological site chronologies were built for each of the 6 sites, and response to climate was evaluated. The long-term δ13C chronologies comprising the period 1800–2008 strongly decline by an average of 2.5‰ from the mid-twentieth century, which corresponds with the commencement of industrialization in Turkey. Oxygen isotope (δ18O) time series show dominantly low undulations, although some high-frequency variations of up to 6‰ are also observed. As a result of latitude and continent effects, oxygen isotope values of tree rings show an average of 3‰ increase from south (Antalya) to the north (Bolu). Correlations between carbon isotope ratios yield high positive values indicating that industrial pollution exerts a major control on the δ13C systematics of the studied trees. Corrected δ13C ratios are mostly represented by strong positive responses to variations in temperature and precipitation, whereas δ18O and summer temperature/precipitation are negatively correlated. Tree-ring widths and δ18O display similar responses to the temperature and sensitivity to the climatic impact of historic volcanic eruptions, and changes in the solar irradiance record are also detected in other high-resolution paleoclimate archives for the region.

Nonlinear detection of paleoclimate-variability transitions possibly related to human evolution

Potential paleoclimatic driving mechanisms acting on human evolution present an open problem of cross-disciplinary scientific interest. The analysis of paleoclimate archives encoding the environmental variability in East Africa during the past 5Ma has triggered an ongoing debate about possible candidate processes and evolutionary mechanisms. In this work, we apply a nonlinear statistical technique, recurrence network analysis, to three distinct marine records of terrigenous dust flux. Our method enables us to identify three epochs with transitions between qualitatively different types of environmental variability in North and East Africa during the (i) Middle Pliocene (3.35-3.15Ma B.P.), (ii) Early Pleistocene (2.25-1.6Ma B.P.), and (iii) Middle Pleistocene (1.1-0.7Ma B.P.). A deeper examination of these transition periods reveals potential climatic drivers, including (i) large-scale changes in ocean currents due to a spatial shift of the Indonesian throughflow in combination with an intensification of Northern Hemisphere glaciation, (ii) a global reorganization of the atmospheric Walker circulation induced in the tropical Pacific and Indian Ocean, and (iii) shifts in the dominating temporal variability pattern of glacial activity during the Middle Pleistocene, respectively. A reexamination of the available fossil record demonstrates statistically significant coincidences between the detected transition periods and major steps in hominin evolution. This result suggests that the observed shifts between more regular and more erratic environmental variability may have acted as a trigger for rapid change in the development of humankind in Africa.

Distichia peat — A new stable isotope paleoclimate proxy for the Andes

Global climate variability is a well-documented fact; however, the human contribution to climate change is now being vigorously debated. Therefore, a better understanding of past natural climate variability may help to establish the actual anthropogenic contribution to the observed climatic trend. A variety of high-resolution proxies now exist for documenting climate variability that has occurred in the northern hemisphere over the last 10 ka. In contrast, high-resolution paleoclimate records are more limited for regions such as high altitudes in the Andes/South America. However, many regions of the Andes contain a rich, but as yet overlooked, paleoclimate archive in the form of thick peat deposited in situ by the Distichia plant. In our study, based on altitudinal transect from the Peruvian Andes, we found a statistically significant and strong relationship between the stable carbon isotope composition of Distichia and air temperature (R = 0.92 p < 0.01). We also confirmed good preservation of relative differences in the original stable carbon isotope composition in peat derived from this plant. Our calibration showed that a decrease of ~ 0.97 ± 0.23‰ in the stable carbon isotope composition of Distichia peat reflects a 1 °C increase in mean air temperature of the growing seasons. This relationship can be used as a new high-resolution proxy for reconstruction of paleotemperature variations over the past several thousand years in the Andes Mountains based on Distichia peat cores.

Abrupt millennial-scale changes in intensity of Southern Hemisphere westerly winds during marine isotope stages 2–4

Research Article| May 01, 2011 Abrupt millennial-scale changes in intensity of Southern Hemisphere westerly winds during marine isotope stages 2–4 Thomas E. Whittaker; Thomas E. Whittaker * 1Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand *Current address: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA; E-mail: twhittak@unm.edu. Search for other works by this author on: GSW Google Scholar Chris H. Hendy; Chris H. Hendy 1Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand Search for other works by this author on: GSW Google Scholar John C. Hellstrom John C. Hellstrom 2School of Earth Sciences, University of Melbourne, VIC 3010, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Thomas E. Whittaker * 1Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand Chris H. Hendy 1Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand John C. Hellstrom 2School of Earth Sciences, University of Melbourne, VIC 3010, Australia *Current address: Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA; E-mail: twhittak@unm.edu. Publisher: Geological Society of America Received: 14 Oct 2010 Revision Received: 12 Dec 2010 Accepted: 14 Dec 2010 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2011 Geological Society of America Geology (2011) 39 (5): 455–458. https://doi.org/10.1130/G31827.1 Article history Received: 14 Oct 2010 Revision Received: 12 Dec 2010 Accepted: 14 Dec 2010 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Thomas E. Whittaker, Chris H. Hendy, John C. Hellstrom; Abrupt millennial-scale changes in intensity of Southern Hemisphere westerly winds during marine isotope stages 2–4. Geology 2011;; 39 (5): 455–458. doi: https://doi.org/10.1130/G31827.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The strength of mid-southern latitude westerly atmospheric circulation plays an important role in global climate. Due to a lack of long, continuous, high-resolution paleoclimate archives from mid-southern latitudes, it remains unclear what factors control changes in its intensity and how past changes affected the climates of landmasses in their path. Here we show growth rate and stable isotope (δ18O, δ13C) profiles from a South Island, New Zealand, stalagmite (HW3) that permit centennial-scale investigation of Southern Hemisphere westerly paleointensity between 73 and 11 ka. Correlation between HW3 growth rate and isotope profiles suggests sensitivity to changes in annual precipitation, a factor controlled by westerly intensity. Low growth rates and relatively enriched isotope ratios define long-term trends in HW3, supporting existing evidence that weaker westerlies predominated during the last glacial period. Abrupt millennial-scale events occur frequently, such that the HW3 record resembles Greenland ice core stable isotope profiles. Furthermore, nearly synchronous timing of nine prominent wet and cool intervals with Heinrich events supports studies showing that increased westerly intensity is closely linked to North Atlantic cooling. As well as Heinrich events, the HW3 profiles also show an Antarctic Cold Reversal–like event during deglaciation, advocating for a bipolar seesaw of global climate at that time. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Mid- to late-Holocene oxygen isotopes from Voldafjorden, western Norway

Basin water in deep-silled Norwegian fjords is primarily influenced by inflowing Atlantic water originating from the Norwegian Atlantic Current (NwAC). Previous studies suggest that benthic foraminiferal oxygen isotope records from such fjords are strongly influenced by variability in this current. The present paper presents a mid- to late-Holocene record (6–2.2 ka) with 17-yr time resolution from a western Norwegian deep-silled fjord, Voldafjorden. An age model, based on ten AMS radiocarbon dates on marine carbonates and on one plant macrofossil, has been established. The study focuses on the oxygen isotope results, obtained from two species of benthic foraminifera: Cassidulina laevigata and Uvigerina mediterranea. The δ18O C. laevigata record has systematically larger amplitudes than the δ18O U. mediterranea record, which most likely is related to different life cycles/periods of calcification. The oxygen isotope results show a clear shift towards higher values between 5 and 4 ka, interpreted to reflect a temperature drop in the basin water of c. 1°C. After the temperature drop, the high frequency variability (centennial and multidecadal) changes abruptly towards larger amplitudes. This corresponds to changes in subperiodicity, where a 370 year cycle in the δ18O C. laevigata record disappears after 3.8 ka. The δ18O transition corresponds to changes in carbon isotopes and grain size distribution, suggesting that a more extensive change in the fjord environment occurred after the cooling. The timing of the oxygen isotope shift towards higher values and the transition in high frequency variability correspond to major changes recorded in paleoclimate archives within the North Atlantic region and globally.

Tephrostratigraphy, chronology and climatic events of the Mediterranean basin during the Holocene: An overview

The identification and characterisation of high-frequency climatic changes during the Holocene requires natural archives with precise and accurate chronological control, which is usually difficult to achieve using only 14C chronologies. The presence of time-spaced tephra beds in Quaternary Mediterranean successions represents an additional, independent tool for dating and correlating different sedimentary archives. These tephra layers are potentially useful for resolving long-standing issues in paleoclimatology and can help towards correlating terrestrial and marine paleoclimate archives. Known major tephras of regional extent derive from central and southern Italy, the Hellenic Arc, and from Anatolia. A striking feature of major Holocene tephra deposition events in the Mediterranean is that they are clustered rather than randomly distributed in time. Several tephra layers occurred at the time of the S1 sapropel formation between c. 8.4 and 9.0 ka BP (Mercato, Gabellotto-Fiumebianco/E1, Cappadocia) and other important tephra layers (Avellino, Agnano Monte Spina, ‘Khabur’ and Santorini/Thera) occurred during the second and third millennia BC, marking an important and complex phase of environmental changes during the mid- to late-Holocene climatic transition. There is great potential in using cryptotephra to overlap geographically Italian volcanic ashes with those originating from the Aegean and Anatolia, in order to connect regional tephrochronologies between the central and eastern Mediterranean.

Magnetostratigraphy and paleoenvironments in shallow-water carbonates: the Oligocene-Miocene sediments of the northern margin of the Liguro-Provençal basin (West Marseille, southeastern France)

AbstractThe present study proposes to estimate the influence of climate, eustatism and local tectonics on the sedimentation of a basin margin at the syn-rift to post-rift transition. For that, paleomagnetic measurements were performed on a marine marly-calcareous sedimentary succession ranging from Upper Oligocene to Lower Miocene and located on the northern margin of the Liguro-Provençal basin. The magnetostratigraphic record is correlated to the reference geomagnetic polarity scale [ATNTS04, Lourens et al. 2004] with the help of biostratigraphy based on calcareous nannofossils and planctonic foraminifers [Oudet et al., 2010]. The resulting age model shows that the 100 m-thick sedimentary succession covers a time span of 5 m.y. from the Late Chattian to the Early Burdigalian. Despite several exposure surfaces and a change in the sedimentation rate, no significant hiatus of sedimentation is documented. In addition, we also estimate the paleoenvironmental evolution through the sedimentary succession. Comparing the dated paleoenvironmental reconstruction with global δ18O and sea level curves [Miller et al., 2005], we show that the Carry-le-Rouet succession is an excellent paleoclimatic archive. Indeed, coral reefs developed at the glacial-interglacial stage transition marking the end of the Oligocene. In addition, the most diversified coral reefs occurred during the warmest period of the Aquitanian. During rifting, bathymetric variations recorded in the studied succession are related to local synsedimentary tectonics whereas, during oceanic crust accretion, global sea level changes influence the sedimentation. This result allows to characterise and to accurately date the break-up unconformity at 20.35 Ma.

Magnetostratigraphic dating of the Huojiadi Paleolithic site in the Nihewan Basin, North China

The fluvio-lacustrine sequences in the Nihewan Basin, northern China provide important terrestrial archives of paleoclimate and paleoenvironment as well as an important source of Paleolithic settlements and therefore early human occupation in the eastern Old World. Magnetostratigraphic dating of the sequences has permitted the precise timing of the basin infilling and associated Paleolithic and mammalian fauna sites. Here we report new magnetostratigraphic results that place stringent age controls on the Huojiadi Paleolithic site in this basin. Partially-oxidized magnetite and hematite were identified as the major carriers for the characteristic remanent magnetizations. Magnetostratigraphic results show that the Huojiadi sequence recorded the very late Matuyama reverse chron and the Jaramillo normal subchron. The stone artifact layer resides in the Jaramillo normal subchron, yielding an estimated age of around 1.0 Ma for the Huojiadi Paleolithic site. Furthermore, by combining our magnetostratigraphy and previously published magnetochronology data, a magnetochronological sequence of the early Pleistocene Paleolithic sites in the Nihewan Basin has been established. The chronological sequence implies that early humans may have persistently colonized the high-latitude temperate areas in the eastern Old World, such as the Nihewan Basin, during the Early Pleistocene.

The importance of sea-level and climate change, including changing wind energy, on the evolution of a coastal estuary: Copano Bay, Texas

123km of high-resolution 2-D seismic lines and 6 sediment cores up to 16m in length were collected from Copano Bay, Texas. These data were used to examine the role of climate and sea-level changes in the evolution of the bay. Paleogeographic maps of the bay were constructed to show how the bay evolved through time. The overall transgression was punctuated by five environmental changes within Copano Bay over the past 9.6ky. The largest environmental change occurred at 8.2ka when the bay-head delta back-stepped approximately 7.5km as a result of a 0.4–1.2m rapid rise in sea level. With a well constrained model of how the bay changed through time, textural data from the most continuous record of middle-bay deposits was used to produce a proxy for wind strength over the last 8.2ky. Our wind strength proxy reveals that Copano Bay experienced relatively tranquil winds during the early Holocene followed by its windiest conditions from 5.2 to 4.1ka and a return to more tranquil winds during the late Holocene. The wind strength proxy was compared with other published paleo-climatic records for the region and a reasonable correlation was found between periods of higher wind energy and drier climate. This study illustrates that despite their complex depositional systems and many sediment and water sources, a system-wide approach to studying an estuary can still be used to extract paleoclimate archives from estuarine deposits.

Scanning reflectance spectroscopy (380–730 nm): a novel method for quantitative high-resolution climate reconstructions from minerogenic lake sediments

High-resolution (annual to sub-decadal) quantitative reconstructions of climate variables are needed from a variety of paleoclimate archives across the world to place current climate change in the context of long-term natural climate variability. Rapid, high-resolution, non-destructive scanning techniques are required to produce such high-resolution records from lake sediments. In this study we explored the potential of scanning reflectance spectroscopy (VIS-RS; 380–730 nm) to produce quantitative summer temperature reconstructions from minerogenic sediments of proglacial, annually laminated Lake Silvaplana, in the eastern Swiss Alps. The scanning resolution was 2 mm, which corresponded to sediment deposition over 1–2 years. We found correlations up to r = 0.84 (p < 0.05) for the calibration period 1864–1950, between six reflectance-dependent variables and summer (JJAS) temperature. These reflectance-dependent variables (e.g. slope of the reflectance 570/630 nm, indicative of illite, biotite and chlorite; minimum reflectance at 690 nm indicative of chlorite) indicate the mineralogical composition of the clastic sediments, which is, in turn, related to climate in the catchment of this particular proglacial lake. We used multiple linear regression (MLR) to establish a calibration model that explains 84% of the variance of summer (JJAS) temperature during the calibration period 1864–1950. We then applied the calibration model downcore to develop a quantitative summer temperature reconstruction extending back to AD 1177. This temperature reconstruction is in good agreement with two independent temperature reconstructions based on documentary data that extend back to AD 1500 and tree ring data that extend back to AD 1177. This study confirms the great potential of in situ scanning reflectance spectroscopy as a novel non-destructive technique to rapidly acquire high-resolution quantitative paleoclimate information from minerogenic lake sediments.