Speleothem master chronologies: combined Holocene O-18 and C-13 records from the North Island of New Zealand and their palaeoenvironmental interpretation

The stable isotope records of four stalagmites dated by 19 TIMS uranium series ages are combined to produce master chronologies for delta(18)O and delta(13)C The delta(18)O records display good overall coherence, but considerable variation in detail. Variability in the delta(13)C records is greater, but general trends can still be discerned. This implies that too fine an interpretation of the structure of individual isotopic records can be unreliable. Speleothem delta(18)O values are demonstrated to show a positive relationship with temperature by comparing trends with other proxy records, but also to respond negatively to rainfall amount. Speleothem delta(13)C is considered to be most influenced by rainfall. The postglacial thermal optimum occur-red around 10.8 ka BP, which is similar in timing to Antarctica but up to 2000 years earlier than most Northern Hemisphere sites. Increasingly negative delta(18)O values after 7.5 ka BP indicate that temperatures declined to a late mid-Holocene minimum centred around 3 ka BP, but more positive values followed to mark a warm peak about 750 years ago which coincided with the 'Mediaeval Warm Period' of Europe. Low 5110 values at 325 years BP suggest cooling coincident with the 'Little Ice Age'. A marked feature of the delta(13)C record is an asymmetric periodicity averaging c. 2250 years and amplitude of c. 1.9parts per thousand. It is concluded that this is mainly driven by waterbalance variations with negative swings representing particularly wet intervals. The 5110 record shows a higher-frequency cyclicity with a period of c. 500 years and an amplitude of c. 0.25 parts per thousand. This is most likely to be temperature-driven, but some swings may have been amplified by precipitation.

Palaeoclimatic implications of the growth history and stable isotope (delta O-18 and delta C-13) geochemistry of a Middle to Late Pleistocene stalagmite from central-western Italy

The age structure and, stable isotope composition of a stalagmite (CC I) from an upland cave in central-western Italy were studied to investigate regional response to global climatic changes. Four growth phases are constrained by 28 thermal ionization and multi-collector inductively coupled plasma mass spectrometry Th-U ages and reveal intermittent deposition through the period between Marine isotope Stage (MIS) 11 and 3 (similar to380 and similar to43 kyr). Most of the growth took place between similar to380 and similar to280 kyr, a period punctuated briefly by a hiatus in deposition through the glacial maximum of MIS 10. Growth was terminated abruptly at 280 kyr just prior to the MIS 8 glacial maximum. With a present-day chamber temperature of 7.5 degreesC, the timing of hiatuses close to these glacial maxima point to freezing conditions at the time. No deposition was recorded through the entirety of MIS 7 and most of MIS 6, whilst two minor growth phases occurred at similar to141-125 and similar to43 kyr. Growth at 141 kyr indicates temperatures >0 degreesC at a time when MIS 6 ice volumes were close to their maximum. High stable carbon isotope (delta(13)C) values (similar to2.8parts per thousand to +3.1parts per thousand) throughout the stalagmite's growth reflect a persistently low input of biogenic CO2, indicating that the steep, barren and alpine-like recharge area of today ha's been in existence for at least the last similar to380 kyr. During MIS 9, the lowest delta(13)C values occur well after maximum interglacial conditions, suggesting a lag in the development of post-glacial soils in this high-altitude karst. The stable oxygen isotope (delta(18)O) trends match the main structural features of the major climate proxy records (SPECMAP, Vostok and Devils Hole), suggesting that the delta(18)O of CC1 has responded to global-scale climate changes, whilst remarkable similarity exists between CC1 delta(18)O and regional sea-surface temperature reconstructions from North Atlantic core ODP980 and southwest Pacific marine core MD97-2120 through the most detailed part of the CC1 record, MIS 9-8. The results suggest that CC1 and other stalagmites from the cave have the potential to capture a long record of regional temperature trends, particularly in regards to the relative severity of Pleistocene glacial stages. (C) 2004 Elsevier B.V. All rights reserved.

Integration of ice-core, marine and terrestrial records for the Australian Last Glacial Maximum and Termination: a contribution from the OZ INTIMATE group

The degree to which Southern Hemisphere climatic changes during the end of the last glacial period and early Holocene (30-8 ka) were influenced or initiated by events occurring in the high latitudes of the Northern Hemisphere is a complex issue. There is conflicting evidence for the degree of hemispheric 'teleconnection' and an unresolved debate as to the principle forcing mechanism(s). The available hypotheses are difficult to test robustly, however, because the few detailed palaeoclimatic records in the Southern Hemisphere are widely dispersed and lack duplication. Here we present climatic and environmental reconstructions from across Australia, a key region of the Southern Hemisphere because of the range of environments it covers and the potentially important role regional atmospheric and oceanic controls play in global climate change. We identify a general scheme of events for the end of the last glacial period and early Holocene but a detailed reconstruction proved problematic. Significant progress in climate quantification and geochronological control is now urgently required to robustly investigate change through this period. Copyright (c) 2006 John Wiley & Sons, Ltd.

Calcium carbonate global LGM Burial rate data

Global databases of calcium carbonate concentrations and mass accumulation rates in Holocene and last glacial maximum sediments were used to estimate the deep-sea sedimentary calcium carbonate burial rate during these two time intervals. Sparse calcite mass accumulation rate data were extrapolated across regions of varying calcium carbonate concentration using a gridded map of calcium carbonate concentrations and the assumption that accumulation of noncarbonate material is uncorrelated with calcite concentration within some geographical region. Mean noncarbonate accumulation rates were estimated within each of nine regions, determined by the distribution and nature of the accumulation rate data. For core-top sediments the regions of reasonable data coverage encompass 67% of the high-calcite (>75%) sediments globally, and within these regions we estimate an accumulation rate of 55.9 ± 3.6 x 10**11 mol/yr. The same regions cover 48% of glacial high-CaCO3 sediments (the smaller fraction is due to a shift of calcite deposition to the poorly sampled South Pacific) and total 44.1 ± 6.0 x 10**11 mol/yr. Projecting both estimates to 100 % coverage yields accumulation estimates of 8.3 x 10**12 mol/yr today and 9.2 x 10**12 mol/yr during glacial time. This is little better than a guess given the incomplete data coverage, but it suggests that glacial deep sea calcite burial rate was probably not considerably faster than today in spite of a presumed decrease in shallow water burial during glacial time.

Planktonic foraminiferal d18O and d13C values, derived sea-surface temperatures from d18O and selected planktonic foraminiferal species for core P69 of Hawke Bay off eastern North Island

Recent evidence suggests that the Subtropical Convergence (STC) zone east of New Zealand shifted little from its modern position along Chatham Rise during the last glaciation, and that offshore surface waters north of the STC zone cooled only slightly. However, at nearshore core site P69 (2195 m depth), 115 km off the east coast of North Island and ca 300 km north of the modern STC zone, planktonic foraminiferal species, transfer function data and stable oxygen and carbon isotope records suggest that surface waters were colder by up to 6°C during the late last glacial period compared to the Holocene, and included a strong upwelling signature. Presently site P69 is bathed by south-flowing subtropical waters in the East Cape Current. The nearshore western end of Chatham Rise supports a major bathymetric depression, the Mernoo Saddle, through which some exchange between northern subtropical and southern subantarctic water presently occurs. It is proposed that as a result of much intensified current flows south of the Rise during the last glaciation, a consequence of more compressed subantarctic water masses, lowered sea level, and an expanded and stronger Westerly Wind system, there was accelerated leakage northwards of both Australasian Subantarctic Water and upwelled Antarctic Intermediate Water over Mernoo Saddle in a modified and intensified Southland Current. The expanded cold water masses displaced the south-flowing warm East Cape Current off southeastern North Island, and offshore divergence was accompanied by wind-assisted upwelling of nutrient-rich waters in the vicinity of P69. A comparable kind of inshore cold water jetting possibly characterised most glacial periods since the latest Miocene, and may account for the occasional occurrence of subantarctic marine fossils in onland late Cenozoic deposits north of the STC zone, rather than invoking wholesale major oscillations of the oceanic STC itself.

(Table 2) Zn/Si ratios for sponge spicules from sediment core samples

The zinc concentration of siliceous sponge spicules was determined from spicules recovered from four sediment cores spanning the last 160 kyr, from the Campbell Plateau region southeast of New Zealand. Zinc/Si results showed little difference between Holocene and glacial aged spicules. An increase in Zn/Si was observed for core Y14, where Zn/Si peaked at about 0.6 ?mol/mol during marine isotope stages 5a-5b. To better understand the role carbon export has on sponge Zn/Si, we explored the strong relationship observed between surficial sediment particulate organic carbon (POC) and the Zn/Si of sponge silica and related this to sediment trap POC flux estimates. Conversion of the Zn/Si records to benthic POC fluxes suggests that there has been little change in the amount of POC reaching Campbell Plateau sediments over the past 30 kyr. These results suggest that surface productivity over the Campbell Plateau has remained relatively low over the past 160 kyr and suggests that glacial productivity was not significantly higher than the present day. Finally, this work reveals that living marine sponges appear to act as the biological equivalents of moored sediment traps, recording the flux of POC to the seafloor by archiving zinc associated with sinking POC in the growing silica skeleton.

(Table 1) Age determination of sediments from the Campbell Plateau

Campbell Plateau occupies a key position in the southwest Pacific sector of the Southern Ocean. The plateau confines and steers the Antarctic Circumpolar Current (ACC) along its flanks, isolating the Subantarctic plateau from cold polar waters. Oxygen and carbon isotope records from Campbell Plateau cores provide new records of water mass stratification for the past 130 kyr. During glacial climes, strengthening of the Subantarctic Front (SAF) caused waters over the plateau flanks to be deeply mixed and ~3°C cooler. Waters of the plateau interior remained stratified and isolated from the cold southern waters. In the west, waters cooled markedly (~4°C) owing to reduced entrainment of Tasman Sea water. Marked cooling also occurred north of Campbell Plateau under increased entrainment of polar water by a branch of the SAF. The ACC remained along the flanks of Campbell Plateau during the last interglacial, when interior waters were stratified and warmer by ~1°C than now.

Radiolarian abundance of sediment core Y8

A high-resolution record of radiolarian faunal changes from Site Y8 south of the Subtropical Front (STF), offshore eastern New Zealand, provides insight into the paleoceanographic history of the last 265 kyrs. Quantitative analysis of radiolarian paleotemperature indicators and radiolarian-based sea surface temperature (SST) estimates reveal distinct shifts during glacial-interglacial (G-I) climate cycles encompassing marine isotope stages (MIS) 8-1. Faunas at Site Y8 are abundant and diverse and consist of a mixture of species typical of the subantarctic, transitional and subtropical zones which is characteristic of subantarctic waters just south of the STF. During interglacials, diverse radiolarian faunas have increased numbers of warm-water taxa (not, vert, similar 15%) while cool-water taxa decrease to not, vert, similar 11% of the assemblage. Warmest climate conditions occurred during MIS 5.5 and the early Holocene Climatic Optimum (HCO) at the onset of MIS 1 where SSTs reach maxima of 12.8 and 12.9 °C, respectively. This suggests that temperatures during the HCO were comparable to the Eemian, one of the warmest interglacial intervals of the Late Quaternary. Glacials are characterized by less diverse radiolarian faunas with cool-water taxa increasing to 49% of the assemblage. Coolest climate conditions occurred in MIS 4 and 2 where SSTs are reduced to 5.4 °C and 4.3 °C, respectively. Radiolarian faunal changes and SST estimates clearly identify major water masses and oceanic fronts in the offshore eastern New Zealand area. During warmest MIS 5.5 and early MIS 1 substantial influence of northern-sourced Subtropical Surface Water (STW) is evident at Site Y8. This implies southward incursions of STW around the eastern crest of Chatham Rise with the STF displaced towards higher latitudes and spinning off eddies as far south as Campbell Plateau. Additionally, increased flow of the Southland Current (SC) might have enhanced the local occurrence of warm-water radiolarians derived from the subtropical Tasman Sea. Coolest glacials are marked by a strong inflow of cool, southern-sourced waters at Site Y8 indicating a more vigorous flow along the Subantarctic Front (SAF).

Benthic foraminifera groups of ODP Site 162-982

The pulsed decline and eventual extinction of 51 species of elongate, cylindrical deep-sea benthic foraminifera (Stilostomellidae, Pleurostomellidae, and some Nodosariidae) occurred at intermediate water depths (1145-2168 m, Sites 980 and 982) in the northern North Atlantic during the mid-Pleistocene transition (MPT, 1.2-0.6 Ma). In the early Pleistocene, prior to their disappearance, these species comprised up to 20% of the total abundance of the benthic foraminiferal assemblage at 2168 m, but up to only 2% at 1145 m. The MPT extinction of 51 species represents ?20% of the total benthic foraminiferal diversity at bathyal depths in the North Atlantic (excluding the myriad of small unilocular forms). The extinction rate during the MPT was approximately 10 species per 0.1 myr, being one or two orders of magnitude greater than normal background turnover rates of deep-sea benthic foraminifera. Comparison of the precise timings of declines and disappearances (= highest occurrences) of each species shows that they were often diachronous between the two depths. The last of these species to disappear in the North Atlantic was Pleurostomella alternans at ~0.679 and ~0.694 Ma in Sites 980 and 982, respectively, which is in good agreement with the previously documented global "Stilostomella extinction" datum within the period 0.7-0.58 Ma. Comparison with similar studies in intermediate depth waters in the Southwest Pacific Gateway indicates that ~61% of the extinct species were common to both regions, and that although the pattern of pulsed decline was similar, the precise order and timing of the extinction of individual species were mostly different on opposite sides of the world. Previous studies have indicated that this extinct group of elongate, cylindrical foraminifera lived infaunally and had their greatest abundances in poorly ventilated, lower oxygen environments. This is supported by our study where there is a strong positive correlation (r = ~+ 0.8) between the flux of the extinction group and low-oxygen/high organic input species (such as Uvigerina, Bulimina and Bolivina) during the MPT, suggesting a close relationship with lower oxygen levels and high food supply to the sea floor. The absolute abundance, flux, and number of the extinction group of species show a progressive withdrawal pattern with major decreases occurring in cold periods with high d13C values. This might be related to increasing chemical ventilation of glacial intermediate water.

(Table 2) Stable carbon and oxygen isotope ratios of foraminifera of DSDP Holes 29-277 and 31-292

Oxygen isotopic studies both of benthic formanifera (Emiliani, 1954, doi:10.1126/science.119.3103.853; Savin et al., 1975, doi:10.1130/0016-7606(1975)86<1499:TMP>2.0.CO;2; Shackleton and Kennett, 1975, doi:10.2973/dsdp.proc.29.117.1975; Savin, 1977, doi:10.1146/annurev.ea.05.050177.001535) and shallow-marine carbonates ( Dorman, 1966; Devereux, 1967; Buchart, 1978, doi:10.1038/275121a0) have provided a useful monitor of marine palaeotemperatures. The Deep Sea Drilling Project (DSDP) has provided cores from many ocean basins to conduct detailed stable isotopic and palaeoceanographic studies of the Cenozoic and late Mesozoic. DSDP Sites 277 and 292, separated by ~60° latitude in Palaeogene times, each record an 18O enrichment in benthic foraminifera of nearly 1 per mil beginning at the Eocene-Oligocene boundary. Planktonic foraminiferal trends are similar to benthic trends in the high latitude southwest Pacific Ocean, but tropical planktonics show only a minor (~0.3 per mil) increase which may reflect a change in seawater composition. These results suggest a sudden cooling of Pacific deep waters and high latitude surface waters forms a useful stratigraphic marker for the Eocene-Oligocene boundary. This boundary is particularly important because of its association with several worldwide palaeo-oceanographic and biogeographic changes. These include a sudden drop in the calcite compensation depth of 1-2 km (van Andel et al., 1975; van Andel, 1975, doi:10.1016/0012-821X(75)90086-2); a decrease in planktonic microfossil diversity (Lipps, 1970, 10.2307/2406711; Kennett, 1978, doi:10.1016/0377-8398(78)90017-8; Sancetta, 1979, doi:10.1016/0377-8398(79)90025-2); a change in planktonic biogeographic patterns (Kennett, 1978, doi:10.1016/0377-8398(78)90017-8; Sancetta, 1979, doi:10.1016/0377-8398(79)90025-2; Haq and Lohmann, 1976, doi:10.1016/0377-8398(76)90008-6); and increased erosion of deep-sea sediments over wide areas (Kennet et al., 1972; Moore et al., 1978).

Stable isotopic composition of Poritres lutea from New Caledonia

A 335 year stable isotope record from a New Caledonia coral (22°S, 166°E) helps fill a large gap in historical climate reconstructions. Although the long-term coral s18O-based sea surface temperature (SST) trend is one of warming, there are notable decadal fluctuations, especially in the early 18th and early 19th centuries. Mean annual SSTs between 1658 and 1900 are estimated to be ~0.3°C lower than the 20th century average, with interdecadal excursions of 0.5°-0.8°C. Time series analyses of the coral isotope record reveals significant concentrations of variance in the El Niño band; an inderdecadal spectral peak is present, but its robustness requires additional statistical evaluation. A secular but irregular decrease in coral d13C values begins in the mid-1800s and may reflect the anthropogenic perturbation of the carbon reservoir. These and other results indicate that the New Caledonia coral isotope record is a valuable source of information on southwest Pacific climate history.

340,000-year centennial-scale marine record of southern hemisphere climatic oscillation

In order to investigate rapid climatic changes at mid-southern latitudes, we have developed centennial-scale paleoceanographic records from the southwest Pacific that enable detailed comparison with Antarctic ice core records. These records suggest close coupling of mid-southern latitudes with Antarctic climate during deglacial and interglacial periods. Glacial sections display higher variability than is seen in Antarctic ice cores, which implies climatic decoupling between mid- and high southern latitudes due to enhanced circum-Antarctic circulation. Structural and temporal similarity with the Greenland ice core record is evident in glacial sections and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations.

Global distributions of diazotrophs nitrogen fixation rates - Depth integrated values computed from a collection of source datasets - Contribution to the MAREDAT World Ocean Atlas of Plankton Functional Types

The MAREDAT atlas covers 11 types of plankton, ranging in size from bacteria to jellyfish. Together, these plankton groups determine the health and productivity of the global ocean and play a vital role in the global carbon cycle. Working within a uniform and consistent spatial and depth grid (map) of the global ocean, the researchers compiled thousands and tens of thousands of data points to identify regions of plankton abundance and scarcity as well as areas of data abundance and scarcity. At many of the grid points, the MAREDAT team accomplished the difficult conversion from abundance (numbers of organisms) to biomass (carbon mass of organisms). The MAREDAT atlas provides an unprecedented global data set for ecological and biochemical analysis and modeling as well as a clear mandate for compiling additional existing data and for focusing future data gathering efforts on key groups in key areas of the ocean. The present data set presents depth integrated values of diazotrophs nitrogen fixation rates, computed from a collection of source data sets.