Climate variability

Grants ALW Theme research Climate Variability

Mid 2002 7 projects were granted in the ALW programme " ALW Theme research Climate Variability"

Propagation of equatorial climate variability of the Southwest Indian Ocean

Main applicant: Prof. dr. W.P.M. de Ruijter
Project staff: Drs. V. Palartanga, Dr. E.J. Machu, Dr. J.J. Nauw-van der Vegt
1-9-2002 31-8-2006
Universiteit Utrecht, Faculteit Natuur- en Sterrenkunde, IMAU

Abstract
From an analysis of satellite altimeter data we have recently found strong evidence for the existence of a large-scale oceanic teleconnection between the monsoon regime and variability in the southwest Indian Ocean. The signal, generated by equatorial wind reversals, propagates through the Indian Ocean by equatorial and coastal Kelvin waves, which trigger Rossby waves that cross the subtropical Indian Ocean. On reaching Madagascar, where flow convergence and focusing of the Rossby waves is observed, ring appear to be formed both in the Mozambique Channel and from the East Madagascar Current. These subsequently drift to the south where they control the shedding of Agulhas rings. The latter rings establish largely the climatically important link between the Indian and Atlantic Oceans. Both the strength of the monsoon system and climate variability related to El Nino and the Indian Ocean Dipole seem to control the amplitude of the signal and eventually the number of rings shed. Around Madagascar, where the si gnal appears to be amplified, we have just completed a series of hydrographic cruises. Moreover, an array of current meter moorings across the narrow section of the Mozambique Channel, spanning a period of almost two years, is about to be recovered. In the first part of this project we aim at combining these in situ observations with the altimetry data to determine the transports through the Mozambique Channel and around Madagascar, including their variability at seasonal to interannual time scales, and to investigate their connection both to local and remote forcing. The latter directly couples it to the second part of the project in which we plan to investigate in detail the propagation of the signal of equatorial climate variability through the Indian Ocean. Using a variety of models of different complexity we plan to focus both on the physical processes that control the dynamics of the teleconnection chain and on its sensitivity to variations in the strength of the equatorial forcing.

Tracing rapid monsoon change across the northwestern Arabian Sea: dust provenance as a monitor of teleconnective climate variation over the last 30 kyr

Main applicant : Prof. dr. D. Kroon
Project staff : Dr. S.J.A. Jung
1-7-2002 - 30-6-2005
Vrije Universiteit Amsterdam, Faculteit der Aard- en Levenswetenschappen (Paleoecology & Paleoclimatology)

Abstract
The tropics are the region of the Earth that receives the highest solar radiation and transfer of this energy to higher latitudes represents the fundamental driving force of the Earth's climate. To help understand the short-term energy transport away from the equator we propose to reconstruct the coupled marine-terrestrial climate across the western Arabian Sea over the last 30,000 years using two high quality sediment cores from strategic locations. Core 905 off Somalia records the coupled West Asian and African monsoon history. In contrast Core 929 off Oman/Yemen is a monitor of climate changes over the Arabian Peninsula currently dominated by north-westerly winds. The most innovative aspect of our approach is the use of Sr-Nd isotope relationships as a proxy of weathering intensity (evaporation-precipitation balance (E-P))1. An initial study of parts of Core 905 demonstrated that Sr-Nd isotopes in the carbinate free clay fraction <2µm are a sensitive proxy of the E-P-balance in Africa (AH P)1. In this proposal we aim to couple radiogenic isotope data with sea surface temperature records down to a decadal time resolution and to focus on four fundamental goals; a) To precisely constrain the repaid temporal and spatial variations during the Holocene, in particular the end of the African Humid Period and the of Early Holocene humid period over the Arabian Peninsula. The aim is to assess, on decadal-centennial time scales whether there are asynchronous climate variations between N-Africa and the Arabian Peninsula; b) To determine the decadal-centennial scale arid-humid cycles in NE- Africa and over the Arabian Peninsula and to establish whether there is a change in amplitude of climate change between the Early and the Late Holocene as suggested for the tropical Atlantic2; c) To assess if there are rapid decadal scale changes in temperature and the E-P-balance over all of the last 30 kyr. The aims of this approach are, to track the extreme and rapid changes in weathering, and any atmospheric reconf i guration (du st provenance variations) during major reorganisations of the climate systems. Specific questions to be addressed are how weathering changed during Heinrich and Dansgaard Oeschger type events and during Termination I; d) The final aim of the project is to assess three teleconnective aspects of climate change: (i) to use single cores to determine the link between marine SST variations and continental weathering, (ii) to reconstruct regional differences in climate change across the western Arabian Sea and (iii) to establish any far field teleconnection between Africa/Arabia, North Atlantic and polar regions.

A new sea surface temperature proxy based on planktonic archaeal membrane lipids, the TEX86

Main applicant : Dr. ir. S. Schouten
Project staff : Mw. M.C. Huguet
Dhr. M.L Woltering
1-1-2003 - 31-3-2007
Royal NIOZ

Abstract
Determination of past sea surface temperatures (SST) is of primary importance for the reconstruction of natural climatic changes. The understanding of these changes is essential if we want to decipher human impact on current global change. Several geochemical proxies for SST reconstructions are used but all have problems and assumptions associated with them. Hence, there is a strong need for more and better SST proxies. We recently developed a new SST proxy (the TEX86) based on the relative distribution of tetraether membrane lipids derived from marine crenarchaeota, a ubiquitous and omnipresent component of marine picoplankton. A preliminary core-top calibration shows a linear relationship of this proxy with SST in the range 0-30°C. Here we propose to further calibrate and validate this new proxy. Small-scale mesocosm experiments, where field populations of marine crenarcheaota are adapted to different temperatures, will be used to further calibrate the TEX86 - SST relationship. In addition, d etermination of the TEX86 in water filtrates and sedimenting particles from different depth and taken at different times of the annual cycle from several selected sites in the ocean will establish which depth interval and part of the annual cycle the temperature reconstructed from the TEX86 reflects. These data will be compared with an extended core-top calibration of the TEX86 - SST relationship. The TEX86 will be further analysed in well-dated cores from the Holocene and Pleistocene and compared with other, previously determined, SST proxies such as the UK37' and the d18O of planktonic foraminifera. This will yield information on SST during different parts of the annual cycle and depth intervals of the water column. These integrated data will likely result in a new, extensively calibrated SST proxy, which is widely applicable in marine sediments.

Does fluctuating solar UV-radiation amplify solar forcing of Holocence climatic shifts? Evidence from a new biological proxy in recent and fossil pollen and spores

Main applicant : Prof. dr. J. Rozema
Project staff : Dr. D. Yeloff, Dr. ing. P. Blokker
1-7-2003 - 31-12-2006
Vrije Universiteit Amsterdam, Faculteit der Aard- en Levenswetenschappen

Abstract
It is hypothesized that fluctuating solar UV-radiation plays an important role in the amplification of relatively small changes in solar activity that cause major Holocene climate shifts. We have developed a new and very sensitive biological proxy that couples the concentration of stable UV-B absorbing compounds (p-coumaric acid in particular) in the sporopollenin fraction of pollen and spores to the amount of UV-B radiation reaching the Earth's surface. This proxy will be used to reconstruct historical UV-B levels during the Holocene and it links these levels with solar activity during periods of abrupt climate change (Preboreal oscillation; transition Subboreal/Subatlantic and climate shifts of the Little Ice Age). Also the p-coumaric acid content of pollen grains and spores from plants of historic herbarium collections (1550-2000) will be analysed. Our approach consists of a) actuo-ecological research (part I) in which the relation of various UV-B radiation levels on p-coumaric acid concentr ations are s tudied in selected plant species (relevant to Part II); and b) paleo-ecological research (Part II) that analyses the fossil record of UV-B in pollen and spores from deposits in relation to evidence for climate change. This approach will be corroborated with other climate proxies such as ?14 C and the local and regional vegetation successions in the same scores. We expect that our study will lead to new insights into solar forcing of Holocene climate change.

Calibration of coccolith chemistry proxis for algal paleo-growth rate: application in the last 30kyrs in the western Arabian Sea upwelling system

Main applicant : Dr. P. Ziveri
Project staff : Dr. P. Ziveri, Drs. S.J.A. Verdegaal
1-6-2002 - 31-5-2005
Vrije Universiteit Amsterdam - Faculteit der Aard- en Levenswetenschappen (Paleoecologie & Paleoklimatologie)

Abstract
With this project we aim to reconstruct algal growth rate and productivity in an upwelling region of the western Arabian Sea. We will use a combination of chemical tracers embedded in the skeletons of coccolithophorids. We will calibrate and apply the new proxies based on oxygen and carbon isotopes and Sr/Ca ratios in monospecific coccolith samples using a recently developed technique. The d18O and Sr/Ca ratios of coccoliths were recently proposed as potential indicators of past growth rates of coccolithophorids on the basis of culture experiments. We will calibrate the new proxies using a unique sediment trap time series off Somalia recording the planktic response to monsoonal-driven seasonal reversalof surface circulation. This area was selected because the Arabian Sea characterized by seasonally high productivity changes. The final goal is to apply the results to a piston core with an exceptional high-resolution temporal record of the last 30 kyrs located at the sediment trap sites.

Tropical environmental change and its teleconnections during the last deglaciation: a lipid biomarker study dated with 14C wiggle-matching.

Main applicant : Dr. G.J.M. Versteegh
Project staff : Ing. M. Rietkerk
1-7-2002 - 15-2-2006
Royal NIOZ

Abstract
Recent investigations point to the tropical ocean to accommodate leading processes at the glacial-interglacial time scale as well as in abrupt climate changes. To test this role of the tropics, we have to reconstruct and interrelate the tropical deglacial environmental changes with other sites on the globe. There are, however, no low-latitude records that are sufficiently accurately dated.. We propose to generate such a chronostratigraphically well controlled reconstruction for the tropical east Atlantic with a 30 yrs resolution. Hereto we apply 1) compound specific 14C measurements of local (marine) and land derived organic biomarkers. and 2) wiggle matching the obtained 14C records with the calibrated 14C record. These measurements are combined with lipid-biomarker data, compound specific stable carbon isotope analyses, and other (e.g. palynomorph and foraminifera-based) proxy records from the same sediments. The combination of data provides 1) essential knowledge about the carbon cycle e.g. with respect to apparent reservoir ages and the responses of marine and terrestrial vegetation to changes in atmospheric pCO2 and sea-level 2) leads and lags compared to well calibrated records of high latitude environmental change (e.g. from ice cores and lakes). The results will be an essential contribution to the understanding of the role of the tropics in rapid global change also with respect to changes induced by humanity (e.g., pCO2).

Holocene and last glacial decadal-to-centennial climate variability from near-equator lake sediments: a multi-proxy and inter-site comparison approach

Main applicant : Prof. dr. H. Hooghiemstra
Project staff : Dr. J.C. Berrio
1-7-2002 - 29-2-2008
Universiteit van Amsterdam - Instituut voor Biodiversiteit en Ecosysteem Dynamica (IBED)

Abstract
This project aims to generate a pollen-based record of climate variability at Decadal-Centennial timescale for the last 80 kyr from Colombian Lake Fuquene (5~0N). Two parallel 60-m cores will be drilled in the centre of the lake. Additional proxies (magnetic susceptibility, sediment analysis, grain size, LOI, stable isotopes, geochemistry, trace elements, diatoms) will be investigated. 3200 pollen samples over the last 80 kyr (25 yr temporal resolution) and 100 AMS 14C-datings in the upper 45 kyr will provide unprecedented accuracy; in the 45-80 kyr interval we use the interstadial series and the position of MIS 4 to match visually curves: Our pilot studies show glacical isotope Stages, Dansgaard-Oeschger cycles and Heinrich events from ice cores can be recognised. We will develop an improved methodology for reconstructing past temperature, moisture, seasonality and general environmental conditions by using a combinations of inverse modelling and more traditional transfer function techniques. R ecords will be thoroughly correlated with marine and ice core records. Frequency analysis may hint climate mechanisms at work, such as ENSO related cycles in dryness. We evaluate interhemispheric connections (leads and lags) and in-between proxy comparisons. Multivariate dat analysis (non-linear calibration), and recently developed plant functional type (PFT)-based analysis of pollen data will be applied to the data set to analyse downcore competition between ecosystems (biomes) and its consequences for temperature reconstructions. This project has a special design: a post-doc (focussing on the interval 35-62 kyr BP) and a PhD student (0-35 kyr BP) will be assisted by an IBED-paid PhD student (62-82 kyr BP). Reaching 80 kyr BP is crucial for time control of the glacial part of the record as pilot studies have shown MIS 4 (with a known age) can be easly detected. After publication this near-equator-based record will be public domain to serve the international community.