Gerald Ganssen

Vrije Universiteit Amsterdam | VU · Department of Earth Sciences

Changeover from a glacial to an interglacial climate is considered as transitional between two stable modes. Palaeoceanographic reconstructions using the polar foraminifera Neogloboquadrina pachyderma highlight the retreat of the Polar Front during the last deglaciation in terms of both its decreasing abundance and stable oxygen isotope values (δ18...

Change-over from a glacial to an interglacial climate is considered as transitional between two stable modes. Palaeoceanographic reconstructions using the polar foraminifera Neogloboquadrina pachyderma highlight the retreat of the polar front during the last deglaciation in terms of both its decreasing abundance and stable oxygen isotope values (δ¹...

The major control upon abundance of planktonic foraminifera and their stable oxygen isotope (δ ¹⁸ O) signature is the seasonally linked variation in water hydrography, key to the proliferation or attenuation of ecologically beneficial constraints. The range and variance σ(δ ¹⁸ O) of planktonic foraminifera can reflect changes in either the season o...

Understanding the vertical distribution and migratory behaviour of shelled holoplanktonic gastropods is essential in determining the environmental conditions to which they are exposed. This is increasingly important in understanding the effects of ocean acidification and climate change. Here we investigated the vertical distribution of atlantid het...

Planktonic foraminifera record oceanic conditions in their shell geochemistry. Many palaeoenvironmental studies have used fossil planktonic foraminifera to constrain past seawater properties by defining species based on their shell morphology. Recent genetic studies, however, have identified ecologically-distinct genotypes within traditionally reco...

So-called "vital effects" are a collective term for a suite of physiologically and metabolically induced variability in oxygen (δ18O) and carbon (δ13C) isotope ratios of planktonic foraminifer shells that hamper precise quantitative reconstruction of past ocean parameters. Correction for potential isotopic offsets from equilibrium or the expected v...

Most planktonic foraminifera migrate vertically through the water column during life, meeting a range of depth-related conditions as they grow and calcify. For reconstructing past ocean conditions from geochemical signals recorded in their shells, it is therefore necessary to know vertical habitat preferences. Species with a shallow habitat and lim...

So called "vital effects", a collective noun for a suite of physiological and metabolic induced variability, in oxygen (δ18O) and carbon (δ13C) isotope ratios of planktonic foraminifer shells hamper precise quantitative reconstruction of past ocean parameters. Correction for potential isotopic offsets from the equilibrium or the expected value is p...

Geochemical and morphological characteristics of Globorotalia truncatulinoides, a deep dwelling planktonic foraminifer, have been used since the mid 1950's to infer (palaeo)oceanographic conditions of the upper ocean. The coiling ratio has been linked to different water masses and stable oxygen isotope signal of this species to changes in depth hab...

Millennial scale climate variability punctuates the record of Northern Hemisphere glacials in the form of Dansgaard–Oeschger cycles. The coldest episodes within these cycles have a marked impact on the location of the Inter-tropical Convergence Zone and thereby the intensity and extent of the Asian monsoon system. Arabian Sea oceanography is closel...

No abstract available.

The fluctuating cover of sea ice and melting glaciers in the North Atlantic region during the most recent three Marine Isotopic Stages (MIS) has been well documented. The consequences of this, either seasonal or perennial ice cover, on oceanographic conditions (i.e. mixing or stratification) has yet to be fully unravelled. Within the scope of the D...

resolution at which foraminiferal stable isotopes are applied in paleo-environmental studies is ever increasing, resulting in continuous sampling of sediment cores. The resolution of such continuously sampled records depends on the rate of sedimentation of foraminiferal shells in its relation to the intensity of bioturbation. Bioturbation essential...

The oxygen isotopic composition of planktonic foraminifera tests is one of the widest used geochemical tools to reconstruct past changes of physical parameters of the upper ocean. It is common practice to analyze multiple individuals from a mono-specific population and assume that the outcome reflects a mean value of the environmental conditions du...

The oxygen isotopic composition of planktonic foraminifera tests is one of the widest used geochemical tools to reconstruct past changes of physical parameters of the upper ocean. It is common practice to analyze multiple individuals from a mono-specific population and assume that the outcome reflects a mean value of the environmental conditions du...

We review important advances in our understanding of the global carbon cycle since the publication of the IPCC AR4. We conclude that: the anthropogenic emissions of CO2 due to fossil fuel burning have increased up through 2008 at a rate near to the high end of the IPCC emission scenarios; there are contradictory analyses whether an increase in atmo...

Periodic intensifications of Antarctic Intermediate Water flow occurred as part of the millennial-scale climate oscillations in the glacial period. During the last glacial period, a profound millennial-scale climate variation pre-vailed. First discovered in Greenland ice cores, it has subsequently been docu-mented around the globe, yet the underly-...

About one third of the anthropogenic carbon dioxide (CO2) released into the atmosphere in the past two centuries has been taken up by the ocean. As CO2 invades the surface ocean, carbonate ion concentrations and pH are lowered. Laboratory studies indicate that this reduces the calcification rates of marine calcifying organisms, including planktic f...

André Berger – many of us have heard of or met this lively figure of the climate scientific community in person. In May 2008 a workshop was organised in Louvain-la-Neuve, Bel-gium, for the occasion of his "official" retirement – of course André will never retire: he was recently awarded an Ad-vanced Research Grant by the European Research Council t...

No abstract available.

About one third of the anthropogenic carbon dioxide (CO2) released into the atmosphere in the past two centuries has been taken up by the ocean. As CO2 invades the surface ocean, carbonate ion concentrations and pH are lowered. Laboratory studies indicate that this reduces the calcification rates of marine calcifying organisms, including planktic f...

Millennial-scale records of planktonic foraminiferal Mg/Ca, bulk sediment U37 K', and planktonic foraminiferal delta 18O are presented across the last two deglaciations in sediment core NIOP929 from the Arabian Sea. Mg/Ca-derived temperature variability during the penultimate and last deglacial periods falls within the range of modern day Arabian S...

During the last glacial period, polar ice cores indicate climate asynchrony between the poles at the millennial time-scale. Yet, surface ocean circulation in large parts of the globe varied in tune with Greenland temperature fluctuations suggesting that any anti-phase behavior to a substantial degree must lie in the deeper global ocean circulation...

Millennial-scale records of planktonic foraminiferal Mg/Ca, bulk sediment UK37', and planktonic foraminiferal d18O are presented across the last two deglaciations in sediment core NIOP929 from the Arabian Sea. Mg/Ca-derived temperature variability during the penultimate and last deglacial periods falls within the range of modern day Arabian Sea tem...

(1) Two sediment cores from the western (905; 10.4690N, 51.5640E, water depth 1586 m) and eastern (SK17; 15150N, 72580E, water depth 840 m) Arabian Sea were used to study past sea surface temperatures (SST) and seawater d18 O( d18Ow) variations for the past 35 ka. We used coupled Mg/Ca-d18O calcite variability in two planktonic foraminiferal specie...

The giant piston core, MD97-2121 (2314-m water depth), collected north of the Subtropical Front, New Zealand, provides a well-dated, stable isotopic record of subtropical and sub-Antarctic influences on the surface and deep ocean over the last deglaciation, especially during the Antarctic Cold Reversal (ACR; ~ 14.1–12.4 ka) and Younger Dryas (YD; 1...

Environmental changes were reconstructed from Lateglacial calcareous gyttja deposits at Gulickshof, southern Netherlands. Analyses of pollen, fresh-water mollusca, stable isotopes and geo-chemistry were performed and the combined evidence was put into a chronostratigraphic framework based on regional biostratigraphy and accelerator mass spectrometr...

To improve our understanding of the Late Pleistocene and Holocene carbonate system of the western Arabian Sea a high-resolution sedimentary record off Somalia has been analysed. The 15.26-m-long piston core 905 comprises a complete record of the last 90,000 years. We have measured concentrations of carbonate minerals, i.e., aragonite, calcite, Mg-c...

The El Niño Southern Oscillation (ENSO) is a climatic phenomenon that affects socio-economical welfare in vast areas in the world. A continuous record of Holocene ENSO related climate variability of the Indo-Pacific Warm pool (IPWP) is constructed on the basis of stable oxygen isotopes in shells of planktic foraminifera from a sediment core in the...

In order to better understand Late Quaternary pelagic aragonite preservation in the western Arabian Sea we have investigated a high-resolution sediment core 905 off Somalia. Pteropod preservation is enhanced in times of reduced monsoon-driven productivity, indicated by low amounts of Corg and low barium to aluminium (Ba/Al) ratios. All periods corr...

The global expression of millennial-scale climatic change during the glacial period and the persistence of this signal in Holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations. We suggest rearrangements in the tropical convection system globally affected the concentration and location of atmosph...

The Asian monsoon is comprised of the Indian and East Asian subsystems. These two components are linked to one another in varying degrees by regions of strong sensible heating (Indo-Asian landmass) and strong latent heat export (the Western Pacific Warm Pool and the southern subtropical Indian Ocean). Variability within the Indian and East Asian su...

In order to better understand Late Quaternary pelagic aragonite preservation in the western Arabian Sea we have investigated a high-resolution sediment core 905 off Somalia. Pteropod preservation is enhanced in times of reduced monsoon-driven productivity, indicated by low amounts of Corg and low barium to aluminium (Ba/Al) ratios. All periods corr...

An increasing number of high-resolution paleoclimate records show substantial natural variation during the Holocene. In order to improve climate projections on human lifetime, the processes that potentially control teleconnections between different parts of the climate system need to be understood. A highly suitable area to study these processes is...

The magnitude of heat and salt transfer between the Indian and Atlantic oceans through 'Agulhas leakage' is considered important for balancing the global thermohaline circulation. Increases or reductions of this leakage lead to strengthening or weakening of the Atlantic meridional overturning and associated variation of North Atlantic Deep Water fo...

The magnitude of heat and salt transfer between the Indian and Atlantic oceans through ‘Agulhas leakage’ is considered important for balancing the global thermohaline circulation1–3. Increases or reductions of this leakage lead to strengthening or weakening of the Atlantic meridional overturning and associated variation of North Atlantic Deep Water...

Transfer of tropical heat to higher latitudes is the major driving force of the Earth’s climate. Consequently, sediments in regions to the north and south of the tropics potentially retain an archive of past major climate reconfigurations. The climate of one such region, around the Arabian Sea, sensitively depends on the coupled Asian and African m...

Uncertainties about the origin of the many disequilibrium or ‘vital effects’ in a variety of calcifying organisms, and whether these effects are constant or variable, have hampered paleoceanographic application of carbon and oxygen isotopic ratios. Unraveling the source of these effects will improve paleoceanographic applications and may provide ne...

Mg/Ca in planktonic foraminifera tests is now well established as a temperature proxy for surface and near-surface waters. Yet work remains to be carried out to define the post-depositional processes affecting foraminiferal Mg/Ca after water-column production. The advantage of Mg/Ca over other paleotemperature proxies is that it can be coupled with...

In a floodplain lake of the Amazon River near the city of Iquitos, northeastern Peru, a one-year monitoring experiment was conducted during which water samples and living bivalves (Anodontites trapesialis) were collected with the aim to investigate seasonal δ18O variation in and fractionation between bivalve aragonite and host water. Both host wate...

An essential prerequisite for predictions of future climate change due to anthropogenic input is a better understanding of the natural processes that control Earth's climate on time scales comparable to human-lifespan of decades to centuries. In particular a better knowledge of the inter-hemispheric phasing of climate events on these time scales ma...

The chemistry of coccoliths serves both as a record of changes in the chemistry of the ocean and as a record of environmental and biological conditions like temperature and productivity. It documents different information than that of foraminiferal carbonate because coccolithophorids, unlike foraminifers, are primary producers. Recently, a breakthr...

Off South Africa, surface and intermediate waters flow from the Indian- to the Atlantic Ocean in the form of Agulhas rings and/or as direct Agulhas leakage. The inter-ocean exchange of water plays a crucial role in the global thermohaline circulation due to the contribution of heat and salt from the Indian to the South Atlantic Ocean. We use the sh...

We analyze the surface d 18 O -salinity relationships of the Bay of Bengal and the Ara-bian Sea, in the northern Indian Ocean, known for their contrasting hydrological conditions. New measurements of these tracers show a very low d 18 O -salinity slope associated with the strong dilution in the Bay of Bengal, but a slope more typical of this latitu...

Hydrographic changes in the NW Arabian Sea are mainly controlled by the monsoon system. This results in a strong seasonal and vertical gradient in surface water properties, such as temperature, nutrients, carbonate chemistry and the isotopic composition of dissolved inorganic carbon (δ13CDIC). Living specimens of the planktic foraminifer species Gl...

An essential prerequisite for the prediction of future climate change due to anthropogenic input is an understanding of the natural processes that control Earth's climate on timescales comparable to human-lifespan. The Early Holocene period was chosen to study the natural climate variability in a warm interval when solar insolation was at its maxim...

The present climate of Thailand is controlled by the Southeast Asian Monsoon system. Different time spans have been suggested for the first monsoon occurrence or intensification, from 30 Ma to the end of the Miocene (8-6 Ma) due to different hypotheses such as (i) Paratethys ocean shrinkage, (ii) Himalayan and Tibetan plateau uplift and (iii) chemi...

NE-Africa and Arabia are foci for early prehistoric civilisations and these regions are controlled by the Asian and African monsoon that are among the most fragile parts of Earth's climate. General links between climate and human prehistoric evo- lution have been proposed but there are few climate data from these regions with a decadal/centennial t...

The primary variability of the composition and properties of seawater is much greater in the shallow coastal zones than in the main body of ocean water. An inadequate understanding of this variability , as well as different diagenetic environments, severely limit the interpretation of the stable-isotope record of shoalwater carbonates. In order to...

The primary variability of the composition and properties of seawater is much greater in the shallow coastal zones than in the main body of ocean water. An inadequate understanding of this variability , as well as different diagenetic environments, severely limit the interpretation of the stable-isotope record of shoalwater carbonates. In order to...

We present a multi-proxy study of sediment Core 905 from the Arabian Sea offshore Somalia to assess the validity of a number of proxies for productivity, temperature and wind strength, to reconstruct the monsoon history in the western Arabian Sea. The present-day seasonal variation in productivity in the modern Arabian Sea off Somalia reflects the...

We present Holocene stable oxygen isotope data from the deep Arabian Sea off Somalia at a decadal time resolution as a proxy for the history of intermediate/upper deep water. These data show an overall δ18O reduction by 0.5‰ between 10 and ˜6.5 kyr B.P. superimposed upon short-term δ18O variations at a decadal-centennial timescale. The amplitude of...

The present climate of Thailand is controlled by the Southeast Asian Monsoon system. Although modeling paleoclimatic fluctuations in monsoon variability has improved, records of past climate changes are crucial to observe the first occurrence or intensification of the monsoon wind system. Different time spans have been suggested from 30 Ma (Ramstei...

1] Abstract: Alkenone-derived estimates of temperature and CO 2 are contributing to our under-standing of Earth's climate history. In order to increase confidence in alkenone-based climate proxies we recommend the following actions. First, the sedimentary component or fraction containing alkenones should be identified in order to assess the impact...

Sr/Ca ratios were measured on eight species of planktonic foraminifera from a core top transect of the North Atlantic. Five of the species (Globigerinoides ruber, Globigerina bulloides, Neogloboquadrina pachyderma, Globigerinoides sacculifer, Globigerinella siphonifera) show remarkably little within-species variability in Sr/Ca (1.2 +/- 0.1%). Thre...

Determining the past record of temperature and salinity of ocean surface waters is essential for understanding past changes in climate, such as those which occur across glacial-interglacial transitions. As a useful proxy, the oxygen isotope composition (δ18O) of calcite from planktonic foraminifera has been shown to reflect both surface temperature...

The stable isotope compositions of the planktonic foraminifera Globigerina bulloides, Globigerinoides ruber (white and pink varieties), Globigerinoides trilobus, Globorotalia inflata and Globorotalia truncatulinoides (right- and left-coiling types) were examined as recorders of North Atlantic surface water properties based on 40 box-core surface se...

Determining the past record of temperature and salinity of ocean surface waters is essential for understanding past changes in climate, such as those which occur across glacial-interglacial transitions. As a useful proxy, the oxygen isotope composition (delta18O) of calcite from planktonic foraminifera has been shown to reflect both surface tempera...

A study of the 140–100ka interval in core T90-9P from the North Atlantic (45° N, 25° W), based on analysis of oxygen and carbon isotope records from planktonic and benthonic foraminifera, and from the bulk sediment fine fraction facilitates a detailed paleoceanographic reconstruction of the penultimate deglaciation (Termination II), and of the Eemi...

Planktic foraminiferal faunas from different environments in the Arabian Sea were size fractionated using 14 sieves with meshes between 100 and 710 μm, to assess the effect of the sieve mesh size cut off level on the faunal composition and to determine the size frequency distribution of individual species. Nine samples from a plankton pump and a to...

The Cretaceous Heterohelix moremani (Cushman) was the only biserial planktonic foraminiferal species from its first appearance in the late Albian up to the Cenomanian/Turonian boundary. Within that time, it increased gradually in abundance relative to other planktonic foraminifera in five Circum-North Atlantic sections. It is generally rare in uppe...

Strontium isotopic ratios and Sr contents of molluscs from the Miocene Pebas Formation in Colombian Amazonia indicate that the bulk of the Pebas Formation was deposited in a freshwater environment, predominantly draining the Andes, with minor contribution from the shield regions. The molluscan oxygen and carbon isotopic composition does not provide...

Existing techniques for estimating natural fluctuations of sea level and global ice-volume from the recent geological past exploit fossil coral-reef terraces or oxygen-isotope records from benthic foraminifera. Fossil reefs reveal the magnitude of sea-level peaks (highstands) of the past million years, but fail to produce significant values for min...

Termination II (glacial to interglacial transition from oxygen isotope stage 6 to stage 5) is considered to be one of the most rapid and abrupt climatic changes during the late Quaternary. Our high resolution geochemical and nannofloral study of the interval from 140 to 100 ka in the northeast Atlantic core T90-9P (45°17.5′N, 25°41.3′W) shows that...