Climatological observations from ship logbooks between 1750 and 1854 (release 2.1)

The Climatological Database for the World's Oceans: 1750-1854 (CLIWOC) project, which concluded in 2004, abstracted more than 280,000 daily weather observations from ships' logbooks from British, Dutch, French, and Spanish naval vessels engaged in imperial business in the eighteenth and nineteenth centuries. These data, now compiled into a database, provide valuable information for the reconstruction of oceanic wind field patterns for this key period that precedes the time in which anthropogenic influences on climate became evident. These reconstructions, in turn, provide evidence for such phenomena as the El Niño-Southern Oscillation and the North Atlantic Oscillation. Of equal importance is the finding that the CLIWOC database the first coordinated attempt to harness the scientific potential of this resource represents less than 10 percent of the volume of data currently known to reside in this important but hitherto neglected source.

dD values of C31 n-alkane (dD wax) from sediment core GeoB9501-4 offshore the Northwest African Sahel

Various studies have demonstrated that the stable hydrogen isotopic composition (dD) of terrestrial leaf waxes tracks that of precipitation (dDprecip) both spatially across climate gradients and over a range of different timescales. Yet, reconstructed estimates of dDprecip and corresponding rainfall typically remain largely qualitative, due mainly to uncertainties in plant ecosystem net fractionation, relative humidity, and the stability of the amount effect through time. Here we present dD values of the C31n-alkane (dDwax) from a marine sediment core offshore the Northwest (NW) African Sahel covering the past 100 years and overlapping with the instrumental record of rainfall. We use this record to investigate whether accurate, quantitative estimates of past rainfall can be derived from our dDwax time series. We infer the composition of vegetation (C3/C4) within the continental catchment area by analysis of the stable carbon isotopic composition of the same compounds (d13Cwax), calculated a net ecosystem fractionation factor, and corrected the dDwax time series accordingly to derive dDprecip. Using the present-day relationship between dDprecip and the amount of precipitation in the tropics, we derive quantitative estimates of past precipitation amounts. Our data show that (a) vegetation composition can be inferred from d13Cwax, (b) the calculated net ecosystem fractionation represents a reasonable estimate, and (c) estimated total amounts of rainfall based on dDwax correspond to instrumental records of rainfall. Our study has important implications for future studies aiming to reconstruct rainfall based on dDwax; the combined data presented here demonstrate that it is feasible to infer absolute rainfall amounts from sedimentary dDwax in tandem with d13Cwax in specific depositional settings.

Accumulation rates of plant-wax-derived long-chain C25 to C35 odd-numbered n-alkanes and d13C values of the n-C31 alkane of ODP Hole 175-1077B

The dominant forcing factors for past large-scale changes in vegetation are widely debated. Changes in the distribution of C4 plants-adapted to warm, dry conditions and low atmospheric CO2 concentrations (Collatz et al., 1998, doi:10.1007/s004420050468) -have been attributed to marked changes in environmental conditions, but the relative impacts of changes in aridity, temperature (Pagani et al., 1999, doi:10.1126/science.285.5429.876; Huang et al., 2001, doi:10.1126/science.1060143) and CO2 concentration (Cerling et al., 1993, doi:10.1038/361344a0; Kuypers et al., 1999, doi:10.1038/20659) are not well understood. Here, we present a record of African C4 plant abundance between 1.2 and 0.45 million years ago, derived from compound-specific carbon isotope analyses of wind-transported terrigenous plant waxes. We find that large-scale changes in African vegetation are linked closely to sea surface temperatures in the tropical Atlantic Ocean. We conclude that, in the mid-Pleistocene, changes in atmospheric moisture content - driven by tropical sea surface temperature changes and the strength of the African monsoon - controlled aridity on the African continent, and hence large-scale vegetation changes.

Geochemical measurements of the Tasmanian Gateway from ODP Hole 189-1172A

Tectonic changes that produced a deep Tasmanian Gateway between Australia and Antarctica are widely invoked as the major mechanism for Antarctic cryosphere growth and Antarctic Circumpolar Current (ACC) development during the Eocene/Oligocene (E/O) transition (34-33 Ma). Ocean Drilling Program (ODP) Leg 189 recovered near-continuous marine sedimentary records across the E/O transition interval at four sites around Tasmania. These records are largely barren of calcareous microfossils but contain a rich record of siliceous- and organic-walled marine microfossils. In this study we integrate micropaleontological, sedimentological, geochemical, and paleomagnetic data from Site 1172 (East Tasman Plateau) to identify four distinct phases (A-D) in the E/O Tasmanian Gateway deepening that are correlative among ODP Leg 189 sites. Phase A, prior to 35.5 Ma: minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes. Phase B, 35.5-33.5 Ma: increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom-water currents. Phase C, 33.5-30.2 Ma: further deepening to bathyal depths, with episodic erosion by increasingly energetic bottom-water currents. Phase D, <30.2 Ma: establishment of stable, open-ocean, warm-temperate, oligotrophic settings characterized by siliceous-carbonate ooze deposition. Our combined evidence indicates that this early Oligocene Tasmanian Gateway deepening initially produced an eastward flow of relatively warm surface waters from the Australo-Antarctic Gulf into the southwestern Pacific Ocean. This "proto-Leeuwin" current fundamentally differs from previous regional reconstructions of eastward flowing cool water (e.g., a "proto-ACC") during the early Oligocene and thereby represents an important new constraint for reconstructing regional- to global-scale dynamics for this major global change event.