Ice Record Research Articles

Sequence of events during the last deglaciation in Southern Ocean sediments and Antarctic ice cores

The last glacial to interglacial transition was studied using down core records of stable isotopes in diatoms and foraminifera as well as surface water temperature, sea ice extent, and ice‐rafted debris (IRD) concentrations from a piston core retrieved from the Atlantic sector of the Southern Ocean. Sea ice is the first variable to change during the last deglaciation, followed by nutrient proxies and sea surface temperature. This sequence of events is independent of the age model adopted for the core. The comparison of the marine records to Antarctic ice CO2 variation depends on the age model as 14C determinations cannot be obtained for the time interval of 29.5–14.5 ka. Assuming a constant sedimentation rate for this interval, our data suggest that sea ice and nutrient changes at about 19 ka B.P. lead the increase in atmospheric pCO2 by approximately 2000 years. Our diatom‐based sea ice record is in phase with the sodium record of the Vostok ice core, which is related to sea ice cover and similarly leads the increase in atmospheric CO2. If gas exchange played a major role in determining glacial to interglacial CO2 variations, then a delay mechanism of a few thousand years is needed to explain the observed sequence of events. Otherwise, the main cause of atmospheric pCO2 change must be sought elsewhere, rather than in the Southern Ocean.

Climatic signals in the last 200 years from stable isotope record in the shells of freshwater snails in Lake Xingcuo, eastern Tibet Plateau, China

Lake Xingcuo is a small closed, hard-water lake, situated on eastern Tibet Plateau. Stable isotope data (δ18O and δ13C) from the freshwater snailGyraulus sibirica (Dunker) in a 34 cm long, radioactive isotope-dated sediment core represent the last 200 years of Lake Xingcuo environmental history. Carbon and oxygen isotope ratios in the shells of the freshwater snail bear information on the isotopic composition of the water in which the shells were formed, which in turn characterizes the climatic conditions prevailing during the snail’s life span. Whole-shell and incremental growth data were collected from modern and fossil shells from Lake Xingcuo. The δ18O values of modern shells from Lake Xingcuo are in equilibrium with those of modern waters, while δ13C values are indicative of snail dietary carbon and a lake with high δ13CTDIC By calibrating δ18O and δ13C in the shellGyraulus sibirica (Dunker) with instrument measured data for the period 1954 – 1992, we found that the δ18O of the snail shells is an efficient indicator to reveal air temperature in the warmer half year instead of that around the whole year, and that there is a certain positive correlation between index δ18O and the running average temperature in the warmer half-year period. Climatic variability on eastern Tibet Plateau, for the last two centuries, has been successfully inferred from the δ18O record in freshwater snails in the sediments of Lake Xingcuo. As such, the last 200 years of palaeoclimatic record for this region can be separated into three periods representing oscillations between warming and cooling, which are confirmed by the Guliya ice record on the Tibet Plateau.

Decadal to millennial cyclicity in varves and turbidites from the Arabian Sea: hypothesis of tidal origin

We have analyzed a Late Holocene record, almost 5000 years long, consisting of varved sediments deposited in the oxygen-minimum zone (OMZ) off Pakistan. We searched for cyclicity in the series of varve thickness (“varve” cycles), of unusually large excursions in varve thickness (“agitation” cycles), and of abundance of turbidites (“turbidite” cycles). We found the following high-frequency cycles (periods between 10 and 100 years) in one or several of the three types of series as follows: near 12.4, 14–15, 16.8, 18.6 (strong, agitation), 25–26 (strong, turbidite), 29–31 (strong, agitation), 39 (varve), 44 (strong, turbidite), 51–54 (strong, agitation), 56 (strong, varve), 64 (strong, turbidite), 69, 77 (strong, turbidite), 82 (very strong, agitation), and 95 years (strong, varve). Low-frequency cycles center around 99–115, 125 (very strong, varve), 164, 177, 202, 242–255 (strong, agitation and turbidite), 280 (strong, varve; doubled, turbidite), 340–370 and 460–490 years. Some cycles of varve thickness match the cyclicity of turbidite frequency (12.3, 14–15, 25–26, 245–255 years) but similarities between spectra are not striking. Taken as a whole, however, the sequence of cycles detected (by autocorrelation and standard Fourier analysis) seems to contain a large proportion of multiples of the basic tidal cycles 4.425 (lunar perigee cycle) and 9.3 years (lunar half-nodal cycle). This impression is supported by testing the three binned spectra for whole-number multiples and fractions as well as whole-number beat structure. We therefore propose that a large proportion of the cyclicity detected can be ascribed to tidal action. Our record also contains evidence for the presence of the 1470-year cycle previously reported from the glacial-age Greenland ice record. The main harmonics of this Greenland cycle can be tied to the pattern of periods seen in the varved sediments. We hypothesize that tidal action produces the cycle, and that the reason for its great length is the requirement that maximum tidal activity has to fall into a narrow seasonal window to be geologically effective.

Radiolarian-based paleotemperatures during the last 160 kyr at ODP Site 1089 (Southern Ocean, Atlantic Sector)

Two cores, Site 1089 (ODP Leg 177) and PS2821-1, recovered from the same location (40°56′S; 9°54′E) at the Subtropical Front (STF) in the Atlantic Sector of the Southern Ocean, provide a high-resolution climatic record, with an average temporal resolution of less than 600 yr. A multi-proxy approach was used to produce an age model for Core PS2821-1, and to correlate the two cores. Both cores document the last climatic cycle, from Marine Isotopic Stage 6 (MIS 6, ca. 160 kyr BP, ka) to present. Summer sea-surface temperatures (SSSTs) have been estimated, with a standard error of ca. ±1.16°C, for the down core record by using Q-mode factor analysis (Imbrie and Kipp method). The paleotemperatures show a 7°C warming at Termination II (last interglacial, transition from MIS 6 to MIS 5). This transition from glacial to interglacial paleotemperatures (with maximum temperatures ca. 3°C warmer than present at the core location) occurs earlier than the corresponding shift in δ 18O values for benthic foraminifera from the same core; this suggests a lead of Southern Ocean paleotemperature changes compared to the global ice-volume changes, as indicated by the benthic isotopic record. The climatic evolution of the record continues with a progressive temperature deterioration towards MIS 2. High-frequency, millennial-scale climatic instability has been documented for MIS 3 and part of MIS 4, with sudden temperature variations of almost the same magnitude as those observed at the transitions between glacial and interglacial times. These changes occur during the same time interval as the Dansgaard–Oeschger cycles recognized in the δ 18O ice record of the GRIP and GISP ice cores from Greenland, and seem to be connected to rapid changes in the STF position in relation to the core location. Sudden cooling episodes (‘Younger Dryas (YD)-type’ and ‘Antarctic Cold Reversal (ACR)-type’ of events) have been recognized for both Termination I (ACR-I and YD-I events) and II (ACR-II and YD-II events), and imply that our core is located in an optimal position in order to record events triggered by phenomena occurring in both hemispheres. Spectral analysis of our SSST record displays strong analogies, particularly for high, sub-orbital frequencies, to equivalent records from Vostok (Antarctica) and from the Subtropical North Atlantic ocean. This implies that the climatic variability of widely separated areas (the Antarctic continent, the Subtropical North Atlantic, and the Subantarctic South Atlantic) can be strongly coupled and co-varying at millennial time scales (a few to 10-ka periods), and eventually induced by the same triggering mechanisms. Climatic variability has also been documented for supposedly warm and stable interglacial intervals (MIS 1 and 5), with several cold events which can be correlated to other Southern Ocean and North Atlantic sediment records.

Have sudden large releases of methane from geological reservoirs occurred since the Last Glacial Maximum, and could such releases occur again?

Methane emissions from geological reservoirs may have played a major role in the sudden events terminating glaciation, both at the start of the Bølling/Allerød and also at the end of the Younger Dryas. These reservoirs include Arctic methane hydrates and also methane hydrate stored in offshore marine sediments in tropical and temperate latitudes. Emissions from hydrate stores may have resonated with tropical wetland emissions, each reinforcing the other. Because methane is such a powerful greenhouse gas, much smaller emissions of methane, compared with carbon dioxide, are required in order to have the same short-term impact by climate forcing. The methane-linked hypothesis has much geological support from sea-floor evidence of emission. However, Greenland ice-core records have been interpreted as showing methane as a consequential factor, rather than the leader, of change. This interpretation can be challenged on the grounds that temperature gradients in Greenland ice record local changes and local timing of a step-like shift in weather fronts, while methane concentrations record changes on a hemispheric and global scale. There are large remaining hydrate reservoirs in the Arctic and in shelf sediments globally, and there is substantial risk of further emissions.

Varves, turbidites and cycles in upper Holocene sediments (Makran slope, northern Arabian Sea)

Abstract We have analysed two Late Holocene records, each about 5 ka long, consisting of varved sediments deposited in the oxygen minimum zone off Pakistan (upper continental slope off Ormara and west of Karachi). Varve counting was checked by accelerator mass spectrometry (AMS) 14 C dating. Detailed lithofacies analysis, ultra-high-resolution X-ray fluorescence scanning, flux rates from sediment traps and the lamina-by-lamina-analysis of a 5 year record (1993–1998) support our interpretation of the annual character of the laminae. Although the pelagic material is deposited throughout the year, most of it is apparently laid down during the high-productivity period of the late summer monsoon. During the winter (mainly mid-December to February-March) mainly light-coloured detrital material (siliciclastic material and reworked carbonate flour) is deposited, probably by river flood events. Event deposits include turbid-plume or suspensate deposits (light grey homogeneous to graded silty clay layers), which are being laid down at decadal or shorter intervals; they are explained by episodically strong river floods after heavy rains transporting mud-charged waters to the narrow shelf and onto the steep continental slope. Medium grey or reddish grey, graded and laminated silt turbidites originated from less frequent, unchannelized, low-density turbidity currents. In general, periods with thin varves (generally correlated with rare turbidites) are correlated with minima of detrital element ratios (TiO 2 /Al 2 O 3 , Zr/Al 2 O 3 , K 2 O/Al 2 O 3 ), especially in Period I ( c. 5600-4700 a bp), suggesting a climate with reduced precipitation and river runoff (possibly winter monsoon dominated). Period II (4700-2600 a bp) is characterized by comparatively thick varves documenting a generally wet period (with possibly summer monsoon domination). During Period III (2600-1000 a bp) a gradual thinning of varves and a decrease of turbidite abundance (thickness) per century is interpreted as a gradual decline of precipitation and river runoff leading finally to dry conditions from 1600 to 1000 a bp. The sequence of cycles detected by autocorrelation and standard Fourier analysis seems to contain a large proportion of multiples of the lunar perigee cycle (4.425 a, 8.85 a) and the lunar (half) nodal cycle (9.3 a, 18.6 a). Our test for cyclicity in the series of varve thickness (varve cycles) and of abundance of turbidites (turbidite cycles) detected prominent high-frequency cycles. Some cycles of varve thickness match the cyclicity of turbidite frequency. We also detected the presence of a 1470 a cycle, previously reported from the glacial-age Greenland ice record.

Atmospheric regime of dust and salt through 75,000 years of Taylor Dome ice core: Refinement by measurement of major, minor, and trace metal suites

Measurement of absolute and relative amounts of dust and salt deposited in the polar ice record is central to several fields of study, including nutrient delivery, atmospheric deposition of trace elements, past wind strengths, dust provenance, and other aspects of climate and geochemical history. We present a method intended to give a more accurate picture than has been possible before of the total amounts and relative proportions of the dust and salt deposited by the atmosphere into polar ice. It also permits us to distinguish different compositional types of dust in the ice. The method is based on precise measurement of a suite of several metals whose proportions contrast strongly between dust and salt and vary substantially between dust types. We apply the method to a small suite of ice samples from the Taylor Dome core in coastal West Antarctica. In full glacial times, when total impurities were high and dust dominated over salt, wind strength in the West Antarctic region was apparently high, and extensive sea‐ice cover prevented incorporation of salt into the atmospheric load. At the termination of the glacial period, increased salt in the dust‐salt mixture indicates that sea ice diminished, but wind strength continued high, and unchanged dust composition indicates unchanged source areas. At about 10,000–11,000 y.B.P., sea‐ice cover appears to have briefly returned to glacial conditions, but wind conditions remained in the milder postglacial condition. Soon after, sea ice retreated, and an abrupt change in dust composition indicates changed source materials or terranes. If extended by analysis of more samples from more sites, such information on salt and dust could provide firm constraints on past wind strengths, extent of sea‐ice cover, deposition fluxes of salt and dust, and changing continental source areas of dust, for both polar regions of the Earth.

Ice record of a 13th century explosive volcanic eruption in northern Victoria Land, East Antarctica

A volcanic event, represented by both coarse ash and a prominent sulphate peak, has been detected at a depth of 85.82 m in a 90 m ice core drilled at Talos Dome, northern Victoria Land. Accurate dating of the core, based on counting annual sulphate and nitrate fluctuations and on comparison with records of major known volcanic eruptions, indicates that the event occurred in 1254 ± 2 AD. The source volcano is most likely to be located within the Ross Sea region. In particular, the glass shards have a trachytic composition similar to rocks from The Pleiades and Mount Rittmann (Melbourne volcanic province), about 200 km from Talos Dome. Sulphate concentration is comparable with that of violent extra-Antarctic explosive events recorded in the same core, but atmospheric perturbation was short-lived and localized, suggesting a negligible impact on regional climate. It is suggested that this eruption may represent the most important volcanic explosion in the Melbourne province during the last eight centuries; thus this event may also represent a valuable chrono-stratigraphical marker on the East Antarctic plateau and in adjoining areas.

Mercury accumulation rates and spatial patterns in lake sediments from west Greenland: a coast to ice margin transect.

The Arctic is recognized as an important focus for long-range transport of contaminants, such as mercury (Hg), from industrial regions at lower latitudes. In addition to large geographic gaps, there are few long-term retrospective time trends in arctic research, besides the Greenland ice record, to assess the onset of atmospheric pollution as well as to establish the rates of change in the terrestrial environment. In a study of sediments from 21 lakes along a 150 km transect from the coast to the ice sheet margin in the Søndre Strømfjord (Kangerlussuaq) region, we present stratigraphic evidence for elevated Hg inputs to this ice-free region on Greenland's west coast. Nineteen study lakes showed Hg concentration enrichments (HgEFconc) in surface compared to deeper sediments, with a mean HgEFconc of 3. Higher HgEFconc are found in lakes closest to the ice margin. The existence of this Hg gradient is supported by pollution Hg inventories in three 210Pb-dated cores. While 210Pb inventories and Pb pollution are higher at the coast, pollution Hg inventories are nearly 3-fold higher at the ice margin (570 micrograms m-2) than at the coast (210 micrograms m-2). These dated cores also indicate an onset of Hg pollution in the region beginning at least by the late 19th century but possibly as early as the 17th century.

First survey of Antarctic sub–ice shelf sediments reveals mid-Holocene ice shelf retreat

The retreat of five small Antarctic Peninsula ice shelves in the late 20th century has been related to regional (possibly anthropogenic) climate warming. We use the record of ice- rafted debris (IRD) in cores to show that the Prince Gustav Channel ice shelf also retreated in mid-Holocene time. Early and late Holocene-age sediments contain IRD derived entirely from local ice drainage basins, which fed the section of ice shelf covering each site. Core- top and mid-Holocene (5–2 ka) sediments include a wider variety of rock types, recording the drift of far-traveled icebergs, which implies seasonally open water at the sites. The period when the Prince Gustav ice shelf was absent corresponds to regional climate warming deduced from other paleoenvironmental records. We infer that the recent decay cannot be viewed as an unequivocal indicator of anthropogenic climate perturbation.

Investigating the anomalous sea-ice conditions in the Canadian High Arctic (Queen Elizabeth Islands) during summer 1998

AbstractThe Queen Elizabeth Islands of the Canadian Arctic Archipelago exhibit one of the most complex sea-ice regimes in the Northern Hemisphere. Time series of minimum monthly passive-microwave sea-ice area (1979−98), minimum sea-ice extent, melting degree-days (1961−98) and minimum sea ice from the new Canadian Ice Service digital database (1968−98) are examined. The extreme nature of the amount of sea-ice melt in the summers of 1998 and 1962 is evident in these time series. The 38 year record of minimum ice, to date, shows no significant trend. Details of the sea-ice behavior during summer 1998 were then examined within 13 individual sea-ice regimes. The multi-year fast-ice plugs in both Sverdrup Channel and Nansen Sound broke up and became truly mobile in 1998. Discussion focuses on the areas surrounding the multi-year plugs, relating sea-ice conditions to weather. Results emphasize the importance of the timing of synoptic events in combination with strong thermal preconditioning in determining the sea-ice conditions in this area during summer 1998.

The ice record of greenhouse gases: a view in the context of future changes

Analysis of air trapped in polar ice provides the most direct information on the natural variability of Greenhouse Trace Gases (GTG). It gives the context for the dramatic change in their atmospheric concentrations induced by anthropogenic activities over the last 200 yr, leading to present-day levels which have been unprecedented over the last 400,000 yr. The GTG ice record also provides insight into the processes generally involved in the interplay between these trace gases and the climate and in particular those which are likely to take place in the next centuries in terms of climate changes and climate feedbacks on ecosystems. The paper gives selected examples of the GTG record, taken during different climatic periods in the past, and illustrating what we can learn in terms of processes.

Spatial distribution of trends and seasonally in the hemispheric sea ice covers: 1978–1996

We extend earlier analyses of a 8.8‐year sea ice data set that described the local seasonal variations and trends in each of the hemispheric sea ice covers to the recently merged 18.2‐year sea ice record from four satellite instruments. The seasonal cycle characteristics remain essentially the same as for the shorter time series, but the local trends are markedly different, in some cases reversing sign. The sign reversal reflects the lack of a consistent long‐term trend and could be the result of localized long‐term oscillations in the hemispheric sea ice covers. By combining the separate hemispheric sea ice records into a global one, we have shown that there are statistically significant net decreases in the sea ice coverage on a global scale. The change in the global sea ice extent is −0.01 ± 0.003 × 106 km2 per decade. The decrease in the areal coverage of the sea ice is only slightly smaller, so that the difference in the two, the ice‐free areas within the packs, has no statistically significant change.

Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica

The recent completion of drilling at Vostok station in East Antarctica has allowed the extension of the ice record of atmospheric composition and climate to the past four glacial–interglacial cycles. The succession of changes through each climate cycle and termination was similar, and atmospheric and climate properties oscillated between stable bounds. Interglacial periods differed in temporal evolution and duration. Atmospheric concentrations of carbon dioxide and methane correlate well with Antarctic air-temperature throughout the record. Present-day atmospheric burdens of these two important greenhouse gases seem to have been unprecedented during the past 420,000 years.

High resolution climate record from the Beijing area during the Last Glacial‐Interglacial Cycle

The Zhaitang loess section, located in the western suburbs of Beijing has yielded a very high resolution magnetic susceptibility record for the last‐glacial and interglacial period. All substages can be clearly defined in marine isotope stage (MIS) 5 (S1) and even also in substage 5a, demonstrating comparable detail with Vostok and parts of the GRIP ice record. Rapid climate shifts during the Eemian period may have extended to continental Asia, but exerted only a weak influence on the Zhaitang record. Abrupt climate transitions (5b/5c/5d/5e) recorded in this section from the NE edge of the Plateau show more detrial than most other Chinese loess records. These three well defined peaks in substage 5a, imply sensitivity of the east Asian monsoon to rapid hemisphere‐scale climate change and the prospect of finding more information on orbital and non‐orbital events in the loess sequence.

Ice record of a large eruption of Deception Island Volcano (Antarctica) in the XVIITH century

A well-marked volcanic ash layer was found at 145.9 m depth in a 154.3 m ice core recovered in 1981 on James Ross Island, Antarctic Peninsula. Ash composition analysis indicates that we are dealing with an eruption of the Deception Island volcano located some 200 km northwestward from James Ross Island. Regional lake sediments seem also to have recorded the eruption. Its date (some 350 years ago) has been determined precisely by comparison with a well-dated South Pole Station ice core. The strength and regional to global impact of the event are discussed. It is concluded it was most probably the largest eruption of this volcano over the studied time period. This exceptional layer was used to adjust the dating of the core.

Opposing Southern Ocean climate patterns as revealed by trends in regional sea ice coverage

The 16.8 year sea ice record (November 1978 to August 1995) derived from satellite passive microwave data shows evidence of contrasting climate patterns in the Southern Ocean as indicated by persistent opposing trends in regional sea ice coverage. Southern Ocean regions adjoining the south Atlantic, south Indian and southwest Pacific Oceans show increasing trends in sea ice coverage, particularly during non-winter months, while regions adjoining the southwest Pacific Ocean show decreasing trends in sea ice coverage, particularly during summer months. The data are compiled from three successive passive microwave sensors from which two separate time-series are analyzed. The first includes the data originally released by the National Snow and Ice Data Center (NSIDC) which have not been significantly adjusted to account for differences in the successive sensors, while the second includes data recently released by NSIDC which have been rigorously adjusted (Cavalieri et al., 1997) to account for differences between sensors. Although the significance of many of the increasing trends detected in the original time-series decrease in the reanalyzed time-series, the overall pattern of contrasting trends remains evident. These trends have important implications for the southern hemisphere heat budget and surface albedo as well as for marine ecosystems associated with various sea ice habitats. Other evidence of contrasting climate patterns with respect to southern hemisphere atmospheric circulation is explored. Due to the relatively short sea ice record, it still remains to be seen whether these trends are natural decadel variation or indicative of global climate change. However, the persistent opposition in Southern Ocean regional ice coverage is noteworthy and may well be studied using global circulation models in order to better define potential positive and negative feedbacks for global change scenarios.

Evidence of recent warming and El Niño‐related variations in ice breakup of Wisconsin lakes

Ice breakup dates from 1968 to 1988 were examined for 20 Wisconsin lakes to determine whether consistent interannual and long‐term changes exist. Each ice record had a trend toward earlier breakup dates, as demonstrated by a negative slope with time, indicating a recent warming trend. The average change in breakup dates was 0.82 d earlier per year for the lakes in southern Wisconsin, which was more extreme than that for the northern Wisconsin lakes (0.45 d yr‒1). Interannual variation in breakup dates was related to the warm phase of El Niño/Southern Oscillation (ENSO) episodes. El Niño events occurred five times during this period (1965, 1972, 1976, 1982, and 1986). Average breakup dates were significantly earlier than average (5–14 d) during the mature phase of El Niño. This variability was affected by the location of the lake: El Niño‐related variation was more evident for the southern lakes than the northern lakes. This difference was caused by the average date of breakup for the southern lakes being in late March directly following the period when air temperatures were strongly related to El Niño events, whereas the average dates of breakup of the northern lakes was in mid‐ to late April following a period when air temperatures were not significantly related to El Niño events. Overall, the interannual and long‐term patterns across Wisconsin were relatively consistent, indicating that recent warming and El Niño‐related variation are regional climatic responses.

High‐resolution ammonium ice core record covering a complete glacial‐interglacial cycle

High‐resolution ammonium measurements were performed along the Greenland Ice Core Program (GRIP) deep ice core, covering a complete climatic cycle. No overall anthropogenic increase is observed over the last 300 years; however, springtime concentrations have roughly doubled since 1950. Biomass burning is estimated to be a major source for ammonia emissions for preindustrial times. It contributes between 10% to 40% to the total ammonium deposited on the central Greenland ice sheet during the Holocene. No correlation is found between the ammonium summer concentrations recorded over the last 100 years and the area burned in northern North America, which is considered to be the main source area for ammonium deposited on the central Greenland ice sheet. This suggests that the meteorological factor is predominant for the pattern of ammonium spikes observed in the ice core. If unchanged meteorological conditions are assumed for the Holocene, as indicated by the δ18O ice record, a decreasing biomass burning activity toward present time can be derived from the ammonium ice record. Soil and vegetation emissions are responsible for the ammonium background concentrations in the ice. The record therefore may be used to trace back the biomass history of the North American continent. A pronounced decreasing trend in background ammonium is found during the Holocene, reflecting decreasing temperature and therefore lower NH3emissions in the source region. Variations in the ammonium concentration during the glacial age are discussed in terms of changes in transport and deposition mechanisms and changes in source strength, which can be related to the extent of the Laurentide ice sheet. The data suggest that the Laurentide ice sheet was built up immediately after the last interglacial and went through several large fluctuations during the last ice age.

Rapid climatic shifts during isotope stages 2–4 in the Polar North Atlantic

Sediment cores from the Polar North Atlantic provide evidence of six periods of sea-ice breakup during isotope stages 4, 3, and 2, probably caused by inflow of North Atlantic surface water into the Polar North Atlantic. These periods are characterized by having a high number of foraminifera/g; they last from 2000 to >10000 yr, and constitute ≈ 50% of the total time span. These periods of sea-ice breakup correlate temporarily to the Heinrich events and the early temperature maximum in the Bond cycles of the North Atlantic and Greenland ice record. Our hypothesis is that massive iceberg discharges that flooded the North Atlantic during each Heinrich event probably triggered an oceanographic regime that gave a much more vigorous surface circulation pattern in the Polar North Atlantic, which contributed to the breakup of the sea-ice cover. Open-water conditions in the Polar North Atlantic are inversely related to terrestrial interstadials of coastal Norway, suggesting ice-sheet starvation during the cold periods and ice-sheet growth when an open-water surface circulation existed in the Polar North Atlantic. Our data document synchronous variations on a October 1900 yr time scale between Arctic oceanic climate, Northern Hemisphere ice-sheet dynamics, and ocean-atmosphere temperature changes.