High-resolution seismic profiles, as well as sedimentological and micropaleontological analyses of three cores, are used to reconstruct the environmental and sedimentological evolution of Preservation Inlet, the southernmost New Zealand fjord. Toward the end of the last glaciation, a series of deep oligotrophic lakes, impounded by shallow sills, occupied Preservation Inlet. Glaciers filled the headwater valleys and the vegetation consisted of a sparse cover of grass, scrub, and shrubs. The principal rivers discharged into the head of these lakes forming large sandy deltas, while finely laminated clays were deposited in the distal basins. As the climate started warming ca. 18,000 yr B.P., the snowline rose and glaciers retreated. Developing forests were dominated by Metrosideros and Cyathea fringed by coastal shrubland. In the now more productive lakes, a rich freshwater fauna developed, sedimentation rates increased, and organic mud accumulated. Under rapidly rising sea level, between 9500 and ca. 8000 yr B.P., the sills enclosing the lakes were successively overtopped. Marine water intruded into the fjord basins and flooded the deltas at the head of the lakes. By 6500 yr B.P. sea level had stabilized and the fjord assumed its present condition. Shrubs decreased in abundance and forests dominated by Weinmannia and Dacrydium cupressinum then developed. A forest dominated by Nothofagus fusca spread between 2000 and 1500 yr B.P., indicating a cooler climate. In Preservation Inlet and other New Zealand fjords, eustatic sea-level rise has been greater than isostatic rebound or tectonic uplift. Coastal inundation has resulted in a transgressional sequence from a limnic to marine environment. This contrasts with fjord coasts of the northern hemisphere where isostatic rebound has produced coastal emergence, or coastal emergence followed by submergence.
A preliminary composite depth section was generated for Site 704 by splicing Holes 704A and 704B together over the interval 0-350 mbsf (0-9 m.y.). High-resolution carbonate and opal data from the cores were correlated with the calcium and silicon signals from the GST logging run in Hole 704B to identify missing and disturbed intervals in the cores. Paleomagnetic and biostratigraphic age boundaries were then transferred to the composite depth records to obtain an age model, and sedimentation rates were calculated by linear interpolation between datums. Algorithms relating measured dry-bulk density to carbonate content and depth were generated to produce predicted values of density for every sample. Accumulation rates of bulk, carbonate, opal, and terrigenous sediment components were then computed to generate a record of sediment deposition on the Meteor Rise that has a resolution of better than 200,000 yr for the period from 8.6 to 1.0 m.y. From 8.6 to 2.5 m.y., bulk-accumulation rates on the Meteor Rise averaged less than 2 g/cm 2 /1000 yr and were dominated by carbonate deposition. The first significant opal deposition (6.0 m.y.) punctuated a brief (less than 0.6 Ma) approach of the Polar Front Zone (PFZ) northward that heralded a period of increasing severity of periodic carbonate dissolution events (terrigenous maxima) that abruptly terminated at 4.8 m.y. (base of the Thvera Subchron), synchronous with the reflooding of the Mediterranean after the Messinian salinity crisis. From 4.8 to 2.5 m.y., carbonate again dominated deposition, and the PFZ was far south except during brief northward excursions bracketing 4.2-3.9, 3.3-2.9, and 2.8-2.7 m.y. At 2.5 m.y., all components of bulk-accumulation rates increased dramatically (up to 15 g/cm 2 /1000 yr), and by 2.4 m.y., a pattern of alternating, high-amplitude carbonate and opal cyclicity marked the initiation of rapid glacial to interglaciál swings in the position of the PFZ, synchronous with the "onset" of major Northern Hemisphere glaciation. Both mass-accumulation rates and the amplitude of the cycles decreased by about 2 m.y., but opal accumulation rates remained high up through the base of the Jaramillo (0.98 m.y.). From 1.9 to 1 m.y., the record is characterized by moderate amplitude fluctuations in carbonate and opal. This record of opal accumulation rates is interpreted as a long-term "Polar Front Indicator" that monitors the advance and retreat of the opal-rich PFZ northward (southward) toward (away from) the Meteor Rise in the subantarctic sector of the South Atlantic Ocean. The timing of PFZ migrations in the subantarctic South Atlantic Ocean is remarkably similar to Pliocene-Pleistocene climate records deduced from benthic oxygen isotope records in the North Atlantic Ocean (
The late Pliocene phase of large-scale climatic deterioration about 3.2-2.4 Ma BP is well documented in a number of (benthic) δ 18 O records. To test the global implications of this event, we have mapped the distribution patterns of various sediment variables in the Pacific and Atlantic Oceans during two time slices, 3.4-3.18 and 2.43-2.33 Ma BP. The changes of bulk sedimentation and bulk sediment accumulation rates are largely explained by the variations of CaCO 3 -accumulation rates (and the accumulation rates of the complementary siliciclastic sediment fraction near continents in higher latitudes). During the late Pliocene, the CaCO 3 -accumulation rate increased along the equatorial Pacific and Atlantic and in the northeastern Atlantic, but decreased elsewhere. The accumulation rate of organic carbon (C org ) and net palaeoproductivity also increased below the high-productivity belts along the equator and the eastern continental margins. From these patterns we may conclude that (trade-) wind- induced upwelling zones and upwelling productivity were much enhanced during that time. This change led to an increased transfer of CO 2 from the surface ocean to the ocean deep water and to a reduction of evaporation, which resulted in an aridification of the Saharan desert belt as depicted in the dust sediments off northwest Africa.
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