Monthly values of the North Atlantic Oscillation Index from 1821 to 2000

Early instrumental pressure measurements from Gibraltar and the Reykjavik area of Iceland have been used to extend to 1821 the homogeneous pressure series at the two locations. In winter the two sites are located close to the centres of action that comprise the North Atlantic Oscillation (NAO). The extended 'winter half-year' record of the NAO enables recent changes in the record to be placed in the context of the period 1823-1996. The period since the early 1970s is the most prolonged positive phase of the oscillation and the late 1980s and early 1990s is the period with the highest values (strongest westerlies). The winter of 1995-1996 marked a dramatic switch in the index, with the change from 1994-1995 being the greatest change recorded from one year to the next since the series began in 1823. (The extended Gibraltar and Reykjavik monthly pressures and the NAO series can be found on the Climatic Research Unit home page, http://www.cru.uea.ac.uk/).

Stable carbon isotope composition of benthic foraminifera from sediments of the Skagerrak, North Sea

The sediment cores 225514 and 225510 were recovered from 420 and 285 m water depth, respectively. They were investigated for their benthic foraminiferal delta13C during the last 500 years. Both cores were recovered from the southern flank of the Skagerrak. The delta13C values of Uvigerina mediterranea and other shallow infaunal species in both cores indicate that organic matter rain rates to the seafloor varied around a mean value until approximately AD 1950 after which they increased. This increase might result from changes in the North Atlantic Current System and a co-occurring persistently high North Atlantic Oscillation index state in the 1980s to 1990s, rather than from anthropogenic eutrophication. Using delta13C mean values of multiple species, we reconstruct delta13C gradients of dissolved inorganic carbon (DIC) within pore waters for the time periods AD 1500 to 1950 and AD 1950 to 2000. The calculated delta13CDIC ranges, interpreted as indicating total organic matter remineralization due to respiration, are generally bigger in Core 225514 than in Core 225510. Since mean delta13C values of U. mediterranea suggest that organic matter rain rates were similar at both locations, differences in total organic matter remineralization are attributed to differing oxygen availability. However, oxygen concentrations in the overlying bottom water masses are not likely to have differed significantly. Thus, we suggest that organic matter remineralization was controlled by oxygen availability within the sediments, reflecting strong differences in sedimentation rates at the two investigated core sites. Based on the assumptions that tests of benthic foraminiferal species inhabiting the same microhabitat depth should show equal delta13C values unless they are affected by vital effects and that Globobulimina turgida records pore water delta13CDIC, we estimate microhabitat-corrected vital effects for several species with respect to G. turgida: >0.7 per mil for Cassidulina laevigata, >1.3 per mil for Hyalinea balthica, and >0.7 per mil for Melonis barleeanus. Melonis zaandami seems to closely record pore water delta13CDIC.

Stable oxygen isotopes of Antarctic snow pits

Stable oxygen analyses and snow accumulation rates from snow pits sampled in the McMurdo Dry Valleys have been used to reconstruct variations in summer temperature and moisture availability over the last four decades. The temperature data show a common interannual variability, with strong regional warmings occurring especially in 1984/85, 1995/96 and 1990/91 and profound coolings during 1977/78, 1983/84, 1988/89, 1993/94, and 1996/97. Annual snow accumulation shows a larger variance between sites, but the early 1970s, 1984, 1997, and to a lesser degree 1990/91 are characterized overall by wetter conditions, while the early and late 1980s show low snow accumulation values. Comparison of the reconstructed and measured summer temperatures with the Southern Oscillation Index (SOI) and the Antarctic Oscillation (AAO) yield statistically significant correlations, which improve when phase-relationships are considered. A distinct change in the phase relationship of the correlation is observed, with the SOI-AAO leading over the temperature records by one year before, and lagging by one year after 1988. These results suggest that over the last two decades summer temperatures are influenced by opposing El Niño Southern Oscillation and AAO forcings and support previous studies that identified a change in the Tropical-Antarctic teleconnection between the 1980s and 1990s.

(Table 1) Physical oceanography from several POLARSTERN cruises to the Arctic Ocean, 1993 - 2012

Freshwater in the Arctic Ocean plays an important role in the regional ocean circulation, sea ice, and global climate. From salinity observed by a variety of platforms, we are able, for the first time, to estimate a statistically reliable liquid freshwater trend from monthly gridded fields over all upper Arctic Ocean basins. From 1992 to 2012 this trend was 600±300 km**3/yr. A numerical model agrees very well with the observed freshwater changes. A decrease in salinity made up about two thirds of the freshwater trend and a thickening of the upper layer up to one third. The Arctic Ocean Oscillation index, a measure for the regional wind stress curl, correlated well with our freshwater time series. No clear relation to Arctic Oscillation or Arctic Dipole indices could be found. Following other observational studies, an increased Bering Strait freshwater import to the Arctic Ocean, a decreased Davis Strait export, and enhanced net sea ice melt could have played an important role in the freshwater trend we observed.

(Appendix table DR1) Foraminiferal distribution data for ODP Hole 178-1098B

Benthic foraminiferal data from Ocean Drilling Program Site 1098 indicate significant changes in deep-water conditions of the Palmer Deep, western Antarctic Peninsula margin, throughout the Holocene (13 ka to present). The earliest Holocene represents a period of transition from the Last Glacial Maximum (LGM). Cold bottom waters, similar to saline shelf water (SSW), dominated the middle Holocene. The late Holocene in the Palmer Deep has been characterized by alternating dominance of circumpolar deep water (CDW) and saline shelf water. These changes have global oceanographic and climatic implications. We suggest that the middle Holocene bottom-water record, in the absence of circumpolar deep water on the western Antarctic Peninsula shelf, indicates high saline shelf water production and/or weakened circumpolar deep water production during the middle Holocene climatic optimum. The late Holocene benthic foraminiferal record indicates rapidly fluctuating sea-ice conditions and may indicate a teleconnection between the South Pacific and Southern Ocean, thus having implications related to the Southern Oscillation Index.

Sea surface temperature oscillations in southern Okinawa Trough during last 2700 years from ODP Hole 195-1202B

Most of the temperature reconstructions for the past two millennia are based on proxy data from various sites on land. Here we present a bidecadal resolution record of sea surface temperature (SST) in Southern Okinawa Trough for the past ca. 2700 years by analyzing tetraether lipids of planktonic archaea in the ODP Hole 1202B, a site under the strong influence of Kuroshio Current and East Asian monsoon. The reconstructed SST anomalies generally coincided with previously reported late Holocene climate events, including the Roman Warm Period, Sui-Tang dynasty Warm Period, Medieval Warm Period, Current Warm Period, Dark Age Cold Period and Little Ice Age. However, the Medieval Warm Period usually thought to be a historical analogue for the Current Warm Period has a mean SST of 0.6-0.8°C lower than that of the Roman Warm Period and Sui-Tang dynasty Warm Period. Despite an increase since 1850 AD, the mean SST in the 20th century is still within the range of natural variability during the past 2700 years. A close correlation of SST in Southern Okinawa Trough with air temperature in East China, intensity of East Asian monsoon and the El-Niño Southern Oscillation index has been attributed to the fluctuations in solar output and oceanic-atmospheric circulation.

Dahlak coral d18O record (DGII) from the southern Red Sea

Coral palaeoclimatic studies are under way at many sites throughout the wet tropics. However, arid environments have received less attention. Here we report a high-resolution, 63 yr record of coral d18O and d13C extracted from a Porites colony from the Dahlak Archipelago, off the Eritrean coast, in the southern Red Sea. The annual cycles of the coral d18O and d13C are inversely related while their inter-annual variations show a strong positive correlation, with similar inter-decadal trends. Inter-annual variations in coral d18O show a relatively weak correlation with the southern Red Sea SST, but are strongly correlated with the Indian Ocean SST, especially on the decadal time-scale. The range of the inter-annual variations in the coral d18O is high compared to changes in local SST, due to the amplifying effect of simultaneous changes in water isotopic composition. Due to this amplification of the climate signal the coral provides a better indication of regional oceangraphic behaviour than the local SST record. The norrtheast monsoon signal in the coral d18O dominates the mean annual signal and shows the best correlation with the instrumental data sets. It appears that variations in the coral d18O are controlled mainly by variations in the intensity of surface water influx from the Indian Ocean to the Red Sea during the winter northeast monsoon. Of particular significance is that the decadal time-scale variations in the coral skeletal d18O are closely correlated with both the Indian Ocean SST and with variations in the Pacific-based Southern Oscillation index. That is, isotopically light coral skeleton, indicating strong NE monsoon Red Sea inflow, correlates with periods of high Indian Ocean SST and with predominantly negative (El Nino) phases of the Southern Oscillation. The simultaneous nature of inter-decadal changes in Asian monsoon and ENSO behaviour suggest pan-Indo-Pacific tropical climate reorganisation and evolution.

Ogasawara winter Sr/Ca and U/Ca data of coral core OGA-02-1 and PDO reconstruction (coral-geoduck index)

The Pacific Decadal Oscillation (PDO), the leading mode of sea surface temperature (SST) anomalies in the extratropical North Pacific Ocean, has widespread impacts on precipitation in the Americas and marine fisheries in the North Pacific. However, marine proxy records with a temporal resolution that resolves interannual to interdecadal SST variability in the extratropical North Pacific are extremely rare. Here we demonstrate that the winter Sr/Ca and U/Ca records of an annually-banded reef coral from the Ogasawara Islands in the western subtropical North Pacific are significantly correlated with the instrumental winter PDO index over the last century. The reconstruction of the PDO is further improved by combining the coral data with an existing eastern mid-latitude North Pacific growth ring record of geoduck clams. The spatial correlations of this combined index with global climate fields suggest that SST proxy records from these locations provide potential for PDO reconstructions further back in time.