Ulrich Salzmann

Palaeoenvironmental changes in the arid and sub arid belt (Sahara-Sahel-Arabian Peninsula) from 150 kyr to present

The PEP III Arid to Subarid Belt includes the largest hot desert in the world, the Sahara- Arabian desert and the Sahel zone. The region of interest extends south of the Atlas Mountains and south and east of the Mediterranean Sea to approximately 10 °N and shows a broadly zonal pattern with a varying seasonal distribution of precipitation. In the north (ca. 20–23 °N), rainfall results from the southward displacement of the midlatitude westerlies during winter whereas the south is governed by seasonal northward migration of the Intertropical Convergence Zone (ITCZ). Contraction and expansion phases of these presently semi-arid to hyper-arid desert areas result from significant changes in local precipitation. Palaeoenvironmental records from Northern Africa (north of 10 °N) and the surrounding seas document long-term changes in the magnitude and extent of the African monsoon in response to orbitally-forced changes in insolation. However, marine records as well as terrestrial palaeohydrological indicators (e.g., lakes, speleothems, rivers, pollen and charcoal) show that there have been changes in the hydrological cycle superimposed on the long-term waxing and waning of the monsoon which cannot be explained exclusively by changes in insolation. These fluctuations in space, time and magnitude were on a regional to continental scale. Here, we review available data on near-surface palaeohydrological indicators and vegetational changes in arid North Africa and the Arabian Peninsula as well as changes in the intensity of the South Asian Monsoon identified from marine sediments of the Arabian Sea. A comparison of regional environmental changes can clarify relations between the environment and changes in the Earth’s climate system. Each data-set is initially presented independently because they represent heteregeneous records from different regions and time periods and thereby emphasise their potential to provide evidence of continental chronostratigraphic palaeoenvironmental changes. Data-sets of lake status and vegetational change are complementary as they strongly reflect hydrological variation. Deep-sea sediments from the Arabian Sea were used to generate continuous records of oceanic upwelling, continental humidity, and dust and river discharge, that are closely related to palaeoenvironmental changes on the surrounding continents.After presenting the individual data-sets we compare the palaeoclimatic reconstructions derived from the different types of evidence.

Sea Surface Temperature of the mid-Piacenzian Ocean: A Data-Model Comparison

The mid-Piacenzian climate represents the most geologically recent interval of long-term average warmth relative to the last million years, and shares similarities with the climate projected for the end of the 21st century. As such, it represents a natural experiment from which we can gain insight into potential climate change impacts, enabling more informed policy decisions for mitigation and adaptation. Here, we present the first systematic comparison of Pliocene sea surface temperature (SST) between an ensemble of eight climate model simulations produced as part of PlioMIP (Pliocene Model Intercomparison Project) with the PRISM (Pliocene Research, Interpretation and Synoptic Mapping) Project mean annual SST field. Our results highlight key regional and dynamic situations where there is discord between the palaeoenvironmental reconstruction and the climate model simulations. These differences have led to improved strategies for both experimental design and temporal refinement of the palaeoenvironmental reconstruction.

The past is a guide to the future? Comparing Middle Pliocene vegetation with predicted biome distributions for the twenty-first century.

During the Middle Pliocene, the Earth experienced greater global warmth compared with today, coupled with higher atmospheric CO2 concentrations. To determine the extent to which the Middle Pliocene can be used as a ‘test bed’ for future warming, we compare data and model-based Middle Pliocene vegetation with simulated global biome distributions for the mid- and late twenty-first century. The best agreement is found when a Middle Pliocene biome reconstruction is compared with a future scenario using 560 ppmv atmospheric CO2. In accordance with palaeobotanical data, all model simulations indicate a generally warmer and wetter climate, resulting in a northward shift of the taiga–tundra boundary and a spread of tropical savannahs and woodland in Africa and Australia at the expense of deserts. Our data–model comparison reveals differences in the distribution of polar vegetation, which indicate that the high latitudes during the Middle Pliocene were still warmer than its predicted modern analogue by several degrees. However, our future scenarios do not consider multipliers associated with ‘long-term’ climate sensitivity. Changes in global temperature, and thus biome distributions, at higher atmospheric CO2 levels will not have reached an equilibrium state (as is the case for the Middle Pliocene) by the end of this century.

The Holocene vegetational history of the Nigerian Sahel based on multiple pollen profiles

Four Holocene pollen diagrams are presented from interdune depressions in the Manga Grasslands (northeastern Nigeria near 13°N). These sequences are interpreted using modern pollen spectra, statistical analyses and groupings based on phytogeographical affinity (Long Distance, Sahelian, Sudanian, Guinean). The roles of climate change and anthropogenic activity in the vegetational history of the central part of Sahel are evaluated. Particular attention is given to the separation of regional (Manga Grasslands) from local (individual depressions) vegetation trends. Humid conditions in the early and mid-Holocene (from 10,000 to ca. 3300 yr B.P.) enabled the establishment of, and sustained, swamp forest vegetation in the interdune depressions. The main taxa (Alchornea, Syzygium and Uapaca) have Guinean affinities. The surrounding dunefields consisted of open savanna with Sahelian and Sudanian (e.g., Combretaceae, Detarium) elements present. Drier conditions ca. 3300 yr B.P. produced abrupt changes in pollen stratigraphy and led to the establishment of the modern vegetation of the Manga Grasslands. Although occupied since at least 3700 yr B.P., there is little evidence of human activity in the pollen diagrams. The nomadic pastoralism practiced by the human occupants of the Manga Grasslands may be palynologically undetectable. Although the Holocene vegetational history of the Manga Grasslands appears to have been primarily controlled by climate, caution should be exercised before drawing climatic inferences from these pollen sequences. For the early and mid-Holocene differences of ca. 1000 years exist in the timing of vegetation changes between the individual depressions. While water levels in the depressions are likely to be coupled to climate, the vegetation response appears to be strongly influenced by local conditions (in particular variations in the depth of depressions and so the relative height of water table). In addition, the Guinean swamp forest vegetation of the early and mid-Holocene is unlikely to be representative of vegetation trends at this latitude, but rather developed extrazonally as a result of the particular topographic/hydrological conditions prevailing in the Manga Grasslands. The problems of lags between climate and vegetation change and the presence of extrazonal vegetation, experienced in the Manga Grasslands, are likely to be common to other Sahelian pollen sites. The palynological information presently available for this zone is deemed insufficient for detailed subcontinental scale reconstructions of vegetation and climate to be attempted.

On the identification of a Pliocene time slice for data–model comparison

The characteristics of the mid-Pliocene warm period (mPWP: 3.264–3.025 Ma BP) have been examined using geological proxies and climate models. While there is agreement between models and data, details of regional climate differ. Uncertainties in prescribed forcings and in proxy data limit the utility of the interval to understand the dynamics of a warmer than present climate or evaluate models. This uncertainty comes, in part, from the reconstruction of a time slab rather than a time slice, where forcings required by climate models can be more adequately constrained. Here, we describe the rationale and approach for identifying a time slice(s) for Pliocene environmental reconstruction. A time slice centred on 3.205 Ma BP (3.204–3.207 Ma BP) has been identified as a priority for investigation. It is a warm interval characterized by a negative benthic oxygen isotope excursion (0.21–0.23‰) centred on marine isotope stage KM5c (KM5.3). It occurred during a period of orbital forcing that was very similar to present day. Climate model simulations indicate that proxy temperature estimates are unlikely to be significantly affected by orbital forcing for at least a precession cycle centred on the time slice, with the North Atlantic potentially being an important exception.

El Niño–Southern Oscillation, Pliocene climate and equifinality

It has been suggested that, during the Pliocene (ca 5–1.8 Ma), an El Niño state existed as a permanent rather than an intermittent feature; that is, the tropical Pacific Ocean was characterized by a much weaker east–west gradient than today. One line of inquiry used to investigate this idea relates modern El Niño teleconnections to Pliocene proxy data by comparing regional differences in precipitation and surface temperature with climate patterns associated with present-day El Niño events, assuming that agreement between Pliocene data and observations of modern El Niño events supports this interpretation. Here, we examine this assumption by comparing outputs from a suite of Mid-Pliocene climate simulations carried out with the UK Met Office climate model. Regional patterns of climate change associated with changes in model boundary conditions are compared with observed El Niño–Southern Oscillation teleconnection patterns. Our results indicate that many of the proposed ‘permanent El Niño’ surface temperature and precipitation patterns are observable in Mid-Pliocene climate simulations even when they display variability in tropical Pacific sea surface temperatures (SSTs) or when forced with a modern east–west SST gradient. Our experiments highlight the possibility that the same outcome may be achieved through different initial conditions (equifinality); an important consideration for reconstructed patterns of regional Mid-Pliocene climate.

Sebkhas as ecological archives and the vegetation and landscape history of southeastern Tunisia during the last two millennia

Sebkhas are temporary lacustrine systems depending on the number and extension of floodings. They may create laminated sediments which can be exploited as ecological archives. Contrary to those of meromictic lakes they are seasonal but not annual. After each flooding a detritus layer and a plasmo-condensed layer of bacteria and algae are formed in the water body or film and during the subsequent dessication a third subaeric layer of evaporites is build up. These laminae show a quasi-textile fabric and they can trap and conserve any dust and fine grained material. A high resolution pollendiagram covering the last two millennia as well as geochemical analysis from a southeastern Tunisian sebkha demonstrate the potentials of these ecological archives.

Changes in Holocene climate and the intensity of Southern Hemisphere Westerly Winds based on a high-resolution palynological record from sub-Antarctic South Georgia

Sub-Antarctic South Georgia is a key region for studying climate variability in the Southern Hemisphere, because of its position at the core of the Southern Hemisphere Westerly Wind belt and between the Antarctic Circumpolar Current and the Polar Frontal Zone. Here, we present a 5.8-m long high-resolution pollen record from Fan Lake on Annenkov Island dominated by local sub-polar vegetation, with Acaena and Poaceae being present throughout the last 7000 years. Palynological and sedimentological analyses revealed a warm late Holocene ‘climate optimum’ between 3790 and 2750 cal. yr BP, which was followed by a gradual transition to cool and wet conditions. This cooling was interrupted by slightly warmer environmental conditions between 1670 and 710 cal. yr BP that partly overlap with the Northern Hemisphere ‘Medieval Climate Anomaly’. Increases in non-native and long-distance pollen grains transported from South America (e.g. Nothofagus, Podocarpus) indicate that stronger Southern Hemisphere Westerly Winds over South Georgia possibly occurred during some ‘colder’ phases of the late Holocene, most notably between c. 2210 and 1670 cal. yr BP and after 710 cal. yr BP.

Palynological Evidence for a Warmer Boreal Climate in the Late Pliocene of the Yukon Territory, Canada

The Late Pliocene (3.6–2.6 Ma) was a period of significant global warmth, considered a potential analogue for future anthropogenic climate change. Newly discovered fine-grained sediments from between the gold-bearing lower and upper White Channel Gravels show the presence of a wetland or lake within Bonanza Creek, Dawson Mining District, Yukon. This environment was surrounded by a diverse Pinaceae-dominated boreal forest with significant stands of angiosperms in favourable sites. Quantitative climate reconstructions derived from pollen and spores reveal a mean annual temperature at least 6 °C warmer than today with warm summers and relatively mild winters. Finally, the new pollen assemblage is used to discuss the age of the White Channel Gravels.

Artisanal Fishery of the Mangrove Crab Ucides cordatus (Ucididae) and First Steps Toward a Successful Co-Management in Bragança, North Brazil

The Braganca district in north Brazil offers a unique opportunity for examining the functioning of a small-scale mangrove crab fishery. North Brazilian mangroves are extensive and the large crab Ucides cordatus is very abundant, even though this slow-growing species has been exploited for decades all year round. Ucides sustains a considerable annual yield of ∼7 tons per km² in this district, and 42% of the rural coastal households are involved in the collection or commercialisation of this crab. We describe capture techniques and main outcomes of 8 years of participatory fisheries monitoring, evaluate the status of the U. cordatus population and characterize the commercialisation of the crabs. The average number of crab collectors working on Braganca peninsula each day was 121 ± 105 (<1 man-day per km² per day; data source 2003). In 2003, their net income was 1.5- to 2.5-fold higher (US