Search results for "paleoclimatology"

A mechanism for brief glacial episodes in the Mesozoic greenhouse

2011

[1] The Mesozoic, perhaps the longest period of warmth during the Phanerozoic Earth history, has been repeatedly affected by short-lived cold interludes lasting about one million years. While the origin of these cold snaps has been classically attributed to a temporary atmospheric CO2 drawdown, quantified mechanisms explaining these instabilities of the carbon cycle are still lacking. Based on a climate carbon cycle model, we show that the general demise of carbonate platforms accompanying these short-lived cold interludes is a powerful mechanism capable of generating a fast atmospheric CO2 decrease and a moderate sea level drop associated with ice sheet buildup. The temporary nature of the…

Vegetation and environmental changes in tropical South America from the last glacial to the Holocene documented by multiple cave sediment proxies

2019

Abstract δ 18 O values in speleothems have been utilized to document past changes in South American monsoon intensity. However, changes in regional vegetation and ecosystems have not been part of this discussion, and other cave proxies such as speleothem δ 13 C values, a useful proxy for vegetation reconstruction, have been neglected due to interpretive complexities. Here we report δ 13 C values and 87Sr/86Sr ratios in stalagmites, together with XRF-derived elemental chemistry, δ 13 Corg values and carbon content from a sedimentary profile from the same cave where the stalagmites were collected. In combination with a previously published δ 18 O record, this enables us to clarify climate and…

A continuous high-resolution dust record for the reconstruction of wind systems in central Europe (Eifel, Western Germany) over the past 133 ka

2009

[1] The last glacial cycle in Central Europe is dominated by processes of aeolian dust transport and accumulation. These dust deposits are preserved in soils and lake sediments and provide detailed information about the climate variability during cold and dry periods. Especially the transitions from warm into cold periods are characterized by turbulent climate conditions. The main problems of terrestrial paleoclimate reconstructions are the completeness of the core material and a sampling resolution. To detect single dust storms we use a particle detection method, which allows high resolution, sub-annual analyses of sediment structures in undisturbed samples. The ELSA (Eifel Laminated Sedim…

Control of Seasonality and Interannual to Centennial Climate Variability in the Caribbean During the Holocene—Combining Coral Records, Stalagmite Rec…

2014

This study aimed at quantifying the amplitudes of seasonality and interannual to centennial climate variability in the Caribbean region throughout the Holocene, by using marine (shallow-water corals) and terrestrial (speleothems) climate archives, and climate model simulations (COSMOS). Sea-surface temperature (SST) variability on interdecadal to multidecadal timescales was more pronounced during the mid-Holocene compared to the late Holocene. The amplitude of the SST annual cycle was within the present-day range throughout most of the last 6,000 years. Exceptions include slightly increased SST seasonality at 6,200 years ago, which can be attributed mainly to insolation forcing on orbital t…

Signals and memory in tree-ring width and density data

2015

It has been suggested that maximum latewood density (MXD) should be used instead of tree-ring width (TRW) data to reconstruct post-volcanic cooling effects. A thorough assessment of high frequency signals and potentially differing memory effects in long MXD and TRW chronologies, in response to large volcanic eruptions, is still missing, however. We here present a compilation of MXD and TRW chronologies from 11 sites in the Northern Hemisphere, covering the past 750+ years, and containing significant June–August temperature signals. Basic assessment of the data using Superposed Epoch Analysis reveals a temporally extended response in TRW, by 2–3 years, to large volcanic eruptions, though pos…

Late Miocene sea surface salinity variability and paleoclimate conditions in the Eastern Mediterranean inferred from coral aragonite δ18O

2009

Abstract Coral skeletons are archives of chemical proxies which enable paleoenvironmental reconstructions to be made at subannual resolution. Stable oxygen isotope ( δ 18 O) ratios of these archives reflect sea surface temperature (SST) as well as the δ 18 O composition of ambient seawater. The δ 18 O seawater composition is not only controlled by global ice build-up, but river discharge and the hydrological balance of evaporation and precipitation, all influencing sea surface salinity (SSS), also play an important role in marginal seas. New sub-annually resolved coral δ 18 O data were measured and evaluated together with published data from reef coral communities of Late Miocene age from C…

Ice age at the Middle–Late Jurassic transition?

2003

A detailed record of sea surface temperatures in the Northern Hemisphere based on migration of marine invertebrate fauna (ammonites) and isotopic thermometry (δ18O values of shark tooth enamel) indicates a severe cooling at the Middle–Late Jurassic transition (MLJT), about 160 Ma ago. The magnitude of refrigeration (1–3°C for lower middle latitudes) and its coincidence in time with an abrupt global-scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time. Ice sheets may have developed over the high-latitude mountainous regions of Far-East Russia. The drastic cooling just post-dated the Middle–Late Callovian widespread dep…

Paleoclimatic changes in the Serravallian record of the Mediterranean area

2004

Late Jurassic (Kimmeridgian–Tithonian) stable isotopes (δ18O, δ13C) and Mg/Ca ratios: New palaeoclimate data from Helmsdale, northeast Scotland

2010

Abstract The data presented here provide the first detailed stable isotope ( δ 18 O, δ 13 C) and geochemical (Mg/Ca) investigation of Kimmeridgian–Tithonian belemnites from the Helmsdale Coast, Scotland, UK. Oxygen and carbon stable isotope values from well preserved specimens range from − 2.8 to + 0.3‰ and from − 2.3 to + 2.8‰ respectively. The oxygen isotope data are consistent with palaeotemperatures of up to 24 °C in the Early Kimmeridgian cymodoce Zone and down to 11 °C in the Mid Tithonian rotunda–fittoni Zones. These estimates are strongly supported by the Mg/Ca data, which also indicate a cooling episode (and very similar palaeotemperatures, 11–22 °C) at this time. The cooling event…

Unraveling environmental histories from skeletal diaries — Advances in sclerochronology

2013

High-resolution proxy archives from aquatic settings are essential to better understand processes and mechanisms of global change. During the last decade, it has become increasingly evident that calcified tissues of bivalve mollusks and cold-water corals, in particular, can significantly increase our knowledge of seasonal to multi-decadal paleoclimate and paleoenvironmental variability in the extratropical oceans and coastal marine settings. Daily, tidal, fortnightly and annual growth patterns of periodically formed skeletal hard parts provide a means to place the proxy record in a precise temporal context. Their extreme longevity coupled with the running similarity between growth increment…