Meteorological measurements from the Fourcade and Polar Club Glacier, Warszawa Icefield, King George Island, West Antarctica

The South Shetland Islands are located at the northern tip of the AP which is among the fastest warming regions on Earth. The islands are especially vulnerable to climate change due to their exposure to transient low-pressure systems and their maritime climate. Surface air temperature increases (2.5K in 50 years) are concurrent with retreating glacier fronts, an increase in melt areas, ice surface lowering and rapid break-up and disintegration of ice shelves. We have compiled a unique meteorological data set for the King George Island (KGI)/Isla 25 de Mayo, the largest of the South Shetland Islands. It comprises high-temporal resolution and spatially distributed observations of surface air temperature, wind directions and wind velocities, as well as glacier ice temperatures in profile with a fully equipped automatic weather station on the Warszawa Icefield, from November 2010 and ongoing. In combination with two long-term synoptic datasets (40 and 10 years, respectively) and NCEP/NCAR reanalysis data, we have looked at changes in the climatological drivers of the glacial melt processes, and the sensitivity of the inland ice cap with regard to winter melting periods and pressure anomalies. The analysis has revealed, a positive trend of 5K over four decades in minimum surface air temperatures for winter months, clearly exceeding the published annual mean statistics, associated to a decrease in mean monthly winter sea level pressure. This concurs with a positive trend in the Southern Annular Mode (SAM) index, which gives a measure for the strength and extension of the Antarctic vortex. We connect this trend with a higher frequency of low-pressure systems hitting the South Shetland Islands during austral winter, bringing warm and moist air masses from lower latitudes. Due to its exposure to the impact of transient synoptic weather systems, the ice cap of KGI is especially vulnerable to changes during winter glacial mass accumulation period. A revision of seasonal changes in adiabatic air temperature lapse rates and their dependency on exposure and elevation has shown a clear decoupling of atmospheric surface layers between coastal areas and the higher-elevation ice cap, showing the higher sensitivity to free atmospheric flow and synoptic changes. Observed surface air temperature lapse rates show a high variability during winter months (standard deviations up to ±1.0K/100 m), and a distinct spatial variability reflecting the impact of synoptic weather patterns. The observed advective conditions bringing warm, moist air with high temperatures and rain, lead to melt conditions on the ice cap, fixating surface air temperatures to the melting point. This paper assesses the impact of large-scale atmospheric circulation variability and climatic changes on the atmospheric surface layer and glacier mass accumulation of the upper ice cap during winter season for the Warszawa Icefield on KGI.

Turbulent flux and meteorological measurements during ARCTEX-2006 campaign

This dataset present result from the DFG- funded Arctic-Turbulence-Experiment (ARCTEX-2006) performed by the University of Bayreuth on the island of Svalbard, Norway, during the winter/spring transition 2006. From May 5 to May 19, 2006 turbulent flux and meteorological measurements were performed on the monitoring field near Ny-Ålesund, at 78°55'24'' N, 11°55'15'' E Kongsfjord, Svalbard (Spitsbergen), Norway. The ARCTEX-2006 campaign site was located about 200 m southeast of the settlement on flat snow covered tundra, 11 m to 14 m above sea level. The permanent sites used for this study consisted of the 10 m meteorological tower of the Alfred Wegener Institute for Polar- and Marine Research (AWI), the international standardized radiation measurement site of the Baseline Surface Radiation Network (BSRN), the radiosonde launch site and the AWI tethered balloon launch sites. The temporary sites - set up by the University of Bayreuth - were a 6 m meteorological gradient tower, an eddy-flux measurement complex (EF), and a laser-scintillometer section (SLS). A quality assessment and data correction was applied to detect and eliminate specific measurement errors common at a high arctic landscape. In addition, the quality checked sensible heat flux measurements are compared with bulk aerodynamic formulas that are widely used in atmosphere-ocean/land-ice models for polar regions as described in Ebert and Curry (1993, doi:10.1029/93JC00656) and Launiainen and Cheng (1995). These parameterization approaches easily allow estimation of the turbulent surface fluxes from routine meteorological measurements. The data show: - the role of the intermittency of the turbulent atmospheric fluctuation of momentum and scalars, - the existence of a disturbed vertical temperature profile (sharp inversion layer) close to the surface, - the relevance of possible free convection events for the snow or ice melt in the Arctic spring at Svalbard, and - the relevance of meso-scale atmospheric circulation pattern and air-mass advection for the near-surface turbulent heat exchange in the Arctic spring at Svalbard. Recommendations and improvements regarding the interpretation of eddy-flux and laser-scintillometer data as well as the arrangement of the instrumentation under polar distinct exchange conditions and (extreme) weather situations could be derived.

Continuous condensation particle (CP) observations from 1984 through 2009 at Neumayer Station, Antacrtica

Continuous condensation particle (CP) observations were conducted from 1984 through 2009 at Neumayer Station under stringent contamination control. During this period, the CP concentration (median 258 1/cm**3) showed no significant long term trend but exhibited a pronounced seasonality characterized by a stepwise increase starting in September and reaching its annual maximum of around 10**3/cm**3 in March. Minimum values below 10**2/cm**3 were observed during June/July. Dedicated time series analyses in the time and frequency domain revealed no significant correlations between inter-annual CP concentration variations and atmospheric circulation indices like Southern Annular Mode (SAM) or Southern Ocean Index (SOI). The impact of the Pinatubo volcanic eruption and strong El Niño events did not affect CP concentrations. From thermodenuder experiments we deduced that the portion of volatile (at 125 °C) and semi-volatile (at 250 °C) particles which could be both associated with biogenic sulfur aerosol, was maximum during austral summer, while during winter non-volatile sea salt particles dominated. During September through April we could frequently observe enhanced concentrations of ultrafine particles within the nucleation mode (between 3 nm and 7 nm particle diameter), preferentially in the afternoon.

Sedimentology and stable isotope record of DSDP Hole 68-503B

Samples from the upper portion of a cyclic pelagic carbonate sediment sequence in Deep-Sea Drilling Project (DSDP) hole 503B (4.0°N, 95.6°W) are the first group to be analyzed for paleoceanographic and paleoclimatic proxy-indicators of ice volume, deep ocean and surface water circulation, and atmospheric circulation in order to resolve the complex origin of the cyclicity. Temporal resolution is taken from the delta18O time scale, most other parameters are calculated in terms of their mass flux to the seafloor. CaCO3 percent in the sediments fluctuates in the well-known Pacific pattern and is higher during glacial times. The fluxes of opal and organic carbon have patterns similar to each other and show a variability of a factor of 2.5 to 4. The longer organic carbon record shows flux maxima during both glacial and interglacial times. The accumulation patterns of both opal and organic carbon suggest that the variability in surface water productivity and/or seafloor preservation of those materials is not simply correlated to glacial or interglacial periods. Eolian dust fluxes are greater during interglacial periods by factors of 2 to 5, indicating that eolian source regions in central and northern South America were more arid during interglacial periods. The record of eolian grain size provides a semiquantitative estimation of the intensity of the transporting winds. The eolian data suggest more intense atmospheric circulation during interglacial periods, opposite to the anticipated results. We interpret this observation as recording the southerly shift of the intertropical convergence zone to the latitude of hole 503B during glaciations.

Annual-layer thickness, d18O and sodium values on Akademii Nauk ice core (AD 900-1998) based on core chronology AN 2012

Understanding recent Arctic climate change requires detailed information on past changes, in particular on a regional scale. The extension of the depth-age relation of the Akademii Nauk (AN) ice core from Severnaya Zemlya (SZ) to the last 1100 yr provides new perspectives on past climate fluctuations in the Barents and Kara seas region. Here, we present the easternmost high-resolution ice-core climate proxy records (d18O and sodium) from the Arctic. Multi-annual AN d18O data as near-surface air-temperature proxies reveal major temperature changes over the last millennium, including the absolute minimum around 1800 and the unprecedented warming to a double-peak maximum in the early 20th century. The long-term cooling trend in d18O is related to a decline in summer insolation but also to the growth of the AN ice cap as indicated by decreasing sodium concentrations. Neither a pronounced Medieval Climate Anomaly nor a Little Ice Age are detectable in the AN d18O record. In contrast, there is evidence of several abrupt warming and cooling events, such as in the 15th and 16th centuries, partly accompanied by corresponding changes in sodium concentrations. These abrupt changes are assumed to be related to sea-ice cover variability in the Barents and Kara seas region, which might be caused by shifts in atmospheric circulation patterns. Our results indicate a significant impact of internal climate variability on Arctic climate change in the last millennium.

Clay mineraology and grain size composition of surface sediments from South Pacific Ocean

The reconstruction of low-latitude ocean-atmosphere interactions is one of the major issues of (paleo-)environmental studies. The trade winds, extending over 20° to 30° of latitude in both hemispheres, between the subtropical highs and the intertropical convergence zone, are major components of the atmospheric circulation and little is known about their long-term variability on geological time-scales, in particular in the Pacific sector. We present the modern spatial pattern of eolian-derived marine sediments in the eastern equatorial and subtropical Pacific (10°N to 25°S) as a reference data set for the interpretation of SE Pacific paleo-dust records. The terrigenous silt and clay fractions of 75 surface sediment samples have been investigated for their grain-size distribution and clay-mineral compositions, respectively, to identify their provenances and transport agents. Dust delivered to the southeast Pacific from the semi- to hyper-arid areas of Peru and Chile is rather fine-grained (4-8 µm) due to low-level transport within the southeast trade winds. Nevertheless, wind is the dominant transport agent and eolian material is the dominant terrigenous component west of the Peru-Chile Trench south of ~ 5°S. Grain-size distributions alone are insufficient to identify the eolian signal in marine sediments due to authigenic particle formation on the sub-oceanic ridges and abundant volcanic glass around the Galapagos Islands. Together with the clay-mineral compositions of the clay fraction, we have identified the dust lobe extending from the coasts of Peru and Chile onto Galapagos Rise as well as across the equator into the doldrums. Illite is a very useful parameter to identify source areas of dust in this smectite-dominated study area.

Match points used for synchronization of NGRIP, GRIP, and GISP2

We here present a synchronization of the NGRIP, GRIP, and GISP2 ice cores based mainly on volcanic events over the period 14.9-32.45 ka b2k (before AD 2000), corresponding to Marine Isotope Stage 2 (MIS 2) and the end of MIS 3. The matching provides a basis for applying the recent NGRIP-based Greenland Ice Core Chronology 2005 (GICC05) time scale to the GRIP and GISP2 ice cores, thereby making it possible to compare the synchronized palaeoclimate profiles of the cores in detail and to identify relative accumulation differences between the cores. Based on the matching, a period of anomalous high accumulation rates in the GISP2 ice core is detected within the period 16.5-18.3 ka b2k. The d18O and [Ca2+] profiles of the three cores are presented on the common GICC05 time scale and generally show excellent agreement across the stadial-interstadial transitions and across the two characteristic dust events in Greenland Stadial 3. However, large differences between the d18O and [Ca2+] profiles of the three cores are seen in the same period as the 7-9% increase in the GISP2 accumulation rate. We conclude that changes of the atmospheric circulation are likely to have occurred in this period, altering the spatial gradients in Greenland and resulting in larger variations between the records.

Isotopic composition of terrestrial plant waxes (dD and d13C of n-alkanes) of sediment core SO188_342 from the Northern Bay of Bengal for the last 18 ka

The Indian Summer Monsoon (ISM) is a major global climatic phenomenon. Long-term precipitation proxy records of the ISM, however, are often fragmented and discontinuous, impeding an estimation of the magnitude of precipitation variability from the Last Glacial to the present. To improve our understanding of past ISM variability, we provide a continuous reconstructed record of precipitation and continental vegetation changes from the lower Ganges-Brahmaputra-Meghna catchment and the Indo-Burman ranges over the last 18,000 years (18 ka). The records derive from a marine sediment core from the northern Bay of Bengal (NBoB), and are complemented by numerical model results of spatial moisture transport and precipitation distribution over the Bengal region. The isotopic composition of terrestrial plant waxes (dD and d13C of n-alkanes) are compared to results from an isotope-enabled general atmospheric circulation model (IsoCAM) for selected time slices (pre-industrial, mid-Holocene and Heinrich Stadial 1). Comparison of proxy and model results indicate that past changes in the dD of precipitation and plant waxes were mainly driven by the amount effect, and strongly influenced by ISM rainfall. Maximum precipitation is detected for the Early Holocene Climatic Optimum (EHCO; 10.5-6 ka BP), whereas minimum precipitation occurred during the Heinrich Stadial 1 (HS1; 16.9-15.4 ka BP). The IsoCAM model results support the hypothesis of a constant moisture source (i.e. the NBoB) throughout the study period. Relative to the pre-industrial period the model reconstructions show 20% more rain during the mid-Holocene (6 ka BP) and 20% less rain during the Heinrich Stadial 1 (HS1), respectively. A shift from C4-plant dominated ecosystems during the glacial to subsequent C3/C4-mixed ones during the interglacial took place. Vegetation changes were predominantly driven by precipitation variability, as evidenced by the significant correlation between the dD and d13C alkane records. When compared to other records across the ISM domain, precipitation and vegetation changes inferred from our records and the numerical model results provide evidence for a coherent regional variability of the ISM from the Last Glacial to the present.

Synchronization of the NGRIP, GRIP, and GISP2 ice cores

We here present a synchronization of the NGRIP, GRIP, and GISP2 ice cores based mainly on volcanic events over the period 14.9-32.45 ka b2k (before AD 2000), corresponding to Marine Isotope Stage 2 (MIS 2) and the end of MIS 3. The matching provides a basis for applying the recent NGRIP-based Greenland Ice Core Chronology 2005 (GICC05) time scale to the GRIP and GISP2 ice cores, thereby making it possible to compare the synchronized palaeoclimate profiles of the cores in detail and to identify relative accumulation differences between the cores. Based on the matching, a period of anomalous high accumulation rates in the GISP2 ice core is detected within the period 16.5-18.3 ka b2k. The d18O and [Ca2+] profiles of the three cores are presented on the common GICC05 time scale and generally show excellent agreement across the stadial-interstadial transitions and across the two characteristic dust events in Greenland Stadial 3. However, large differences between the d18O and [Ca2+] profiles of the three cores are seen in the same period as the 7-9% increase in the GISP2 accumulation rate. We conclude that changes of the atmospheric circulation are likely to have occurred in this period, altering the spatial gradients in Greenland and resulting in larger variations between the records.

Mineralogy of the clay fraction from Cenozoic Strata at DSDP Leg 94

Leg 94 Sites are located in a large geographic area of the northeastern Atlantic. Clay mineral analyses of the sediments recovered on Leg 94 (Eocene to the present), together with results obtained from previous DSDP legs (47B, 48, 80, 81, 82), provide greater insight into the paleoenvironmental evolution of the northeastern Atlantic. The characteristics of Eocene clay sediments are regional, reflecting, in the absence of strong bottom currents, the influence of neighboring petrographic environments: basic volcanic rocks (Sites 403-406, 552, and 608) and acid volcanic rocks (Sites 508 to 510). During the Oligocene, atmospheric circulation patterns left their mineralogical signatures in the southern part of the area investigated (Sites 558 and 608), whereas during the Miocene the intrusion of northern water masses led to the gradual homogenization of the clay sedimentation throughout the North Atlantic. In the late Pliocene, input from glacial sources became widespread.

Late Cenozoic eolian dust accumulation in the eastern equatorial Pacific Ocean

Sediments recovered during Ocean Drilling Program (ODP) Leg 138 in the eastern equatorial Pacific Ocean were analyzed for variations in eolian accumulation rate and mean grain-size. Latitudinal and temporal patterns of these parameters showed important changes in the intensity of atmospheric circulation and eolian flux associated with the intertropical convergence zone (ITCZ) and suggested that eolian input parameters could be used to define its paleoposition through time. Modern atmospheric circulation in the equatorial region is weakest in the intertropical convergence zone and increases as the trade winds are approached to the north and south. Thus, the expected spatial pattern of eolian grain size would have the finest material deposited beneath the ITCZ and a coarsening of material in both directions away from this zone. Sediments from ODP Leg 138 show this pattern for much of the Pleistocene and Pliocene but, prior to about 4 Ma, begin to lose the northern coarse component suggesting that the ITCZ was located north of its present position during the late Miocene. Eolian flux records also show a latitudinal pattern of deposition associated with the position of the ITCZ that, similar to eolian grain-size variability, suggests a more northerly position of the ITCZ during the late Miocene. Overall, the regional input of eolian material to the equatorial Pacific has decreased throughout the late Neogene. This reduction in eolian input reflects climatic changes to relatively wetter conditions in the continental eolian source regions beginning during the late Pliocene.

Age determination of sediment core MD99-2201

A marine sediment core from the leeward margin of Great Bahama Bank (GBB) was subjected to a multiproxy study. The aragonite dominated core MD992201 comprises the past 7230 years in a decadal time resolution and shows sedimentation rates of up to 13.8 m/kyr. Aragonite mass accumulation rates, age differences between planktonic foraminifera and aragonite sediments, and temperature distribution are used to deduce changes in aragonite production rates and paleocurrent strengths. Aragonite precipitation rates on GBB are controlled by exchange of carbonate ions and CO2 loss due to temperature-salinity conditions and biological activity, and these are dependent on the current strength. Paleocurrent strengths on GBB show high current velocities during the periods 6000-5100 years BP, 3500-2700 years BP, and 1600-700 years BP; lower current speeds existed during the time intervals 5100-3500 years BP, 2700-1600 years BP, and 700-100 years BP. Bahamian surface currents are directly linked to the North Atlantic atmospheric circulation, and thus periods with high (low) current speeds are proposed to be phases of strong (weak) atmospheric circulation.

Three time-slice simulations of the Eemian (eem), the mid-Holocene (hol), and a pre-industrial (pri) control run with the coupled atmosphere-ocean-model ECHAM5/MPI-OM

Orbital forcing does not only exert direct insolation effects, but also alters climate indirectly through feedback mechanisms that modify atmosphere and ocean dynamics and meridional heat and moisture transfers. We investigate the regional effects of these changes by detailed analysis of atmosphere and ocean circulation and heat transports in a coupled atmosphere-ocean-sea ice-biosphere general circulation model (ECHAM5/JSBACH/MPI-OM). We perform long term quasi equilibrium simulations under pre-industrial, mid-Holocene (6000 years before present - yBP), and Eemian (125 000 yBP) orbital boundary conditions. Compared to pre-industrial climate, Eemian and Holocene temperatures show generally warmer conditions at higher and cooler conditions at lower latitudes. Changes in sea-ice cover, ocean heat transports, and atmospheric circulation patterns lead to pronounced regional heterogeneity. Over Europe, the warming is most pronounced over the north-eastern part in accordance with recent reconstructions for the Holocene. We attribute this warming to enhanced ocean circulation in the Nordic Seas and enhanced ocean-atmosphere heat flux over the Barents Shelf in conduction with retreat of sea ice and intensified winter storm tracks over northern Europe.

Salinity estimation from Gulf of Guinea, sediment core MD03-2707

The isotopic composition of surface seawater is widely used to infer past changes in sea surface salinity using paired foraminiferal Mg/Ca and d18O from marine sediments. At low latitudes, paleosalinity reconstructions using this method have largely been used to document changes in the hydrological cycle. This method usually assumes that the modern seawater d18O (d18Osw)/salinity relationship remained constant through time. Modelling studies have shown that such assumptions may not be valid because large-scale atmospheric circulation patterns linked to global climate changes can alter the seawater d18Osw/salinity relationship locally. Such processes have not been evidenced by paleo-data so far because there is presently no way to reconstruct past changes in the seawater d18Osw/salinity relationship. We have addressed this issue by applying a multi-proxy salinity reconstruction from a marine sediment core collected in the Gulf of Guinea. We measured hydrogen isotopes in C37:2 alkenones (dDa) to estimate changes in seawater dD. We find a smooth, long-term increase of ~10 per mil in dDa between 10 and 3 kyr BP, followed by a rapid decrease of ~10 per mil in dDa between 3 kyr BP and core top to values slightly lighter than during the early Holocene. Those features are inconsistent with published salinity estimations based on d18Osw and foraminiferal Ba/Ca, as well as nearby continental rainfall history derived from pollen analysis. We combined dDa and d18Osw values to reconstruct a Holocene record of salinity and compared it to a Ba/Ca-derived salinity record from the same sedimentary sequence. This combined method provides salinity trends that are in better agreement with both the Ba/Ca-derived salinity and the regional precipitation changes as inferred from pollen records. Our results illustrate that changes in atmospheric circulation can trigger changes in precipitation isotopes in a counter-intuitive manner that ultimately impacts surface salinity estimates based on seawater isotopic values. Our data suggest that the trends in Holocene rainfall isotopic values at low latitudes may not uniquely result from changes in local precipitation associated with the amount effect.