[1] We present a 53-Myr stack (the “LR04” stack) of benthic δ18O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm This is the first benthic δ18O stack composed of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene We also present a new LR04 age model for the Pliocene-Pleistocene derived from tuning the δ18O stack to a simple ice model based on 21 June insolation at 65°N Stacked sedimentation rates provide additional age model constraints to prevent overtuning Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 53 Myr and in the precession band for more than half of the record The LR04 stack contains significantly more variance in benthic δ18O than previously published stacks of the late Pleistocene as the result of higher-resolution records, a better alignment technique, and a greater percentage of records from the Atlantic Finally, the relative phases of the stack's 41- and 23-kyr components suggest that the precession component of δ18O from 27–16 Ma is primarily a deep-water temperature signal and that the phase of δ18O precession response changed suddenly at 16 Ma

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A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records

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.

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

/pdf/climate-and-atmospheric-history-of-the-past-420-000-years-2jdtde1xna.pdf

RECENT results1,2 from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent during the late stages of the last glaciation, suggesting that climate in the North Atlantic region is able to reorganize itself rapidly, perhaps even within a few decades. Here we present a detailed stable-isotope record for the full length of the Greenland Ice-core Project Summit ice core, extending over the past 250 kyr according to a calculated timescale. We find that climate instability was not confined to the last glaciation, but appears also to have been marked during the last interglacial (as explored more fully in a companion paper3) and during the previous Saale–Holstein glacial cycle. This is in contrast with the extreme stability of the Holocene, suggesting that recent climate stability may be the exception rather than the rule. The last interglacial seems to have lasted longer than is implied by the deep-sea SPECMAP record4, in agreement with other land-based observations5,6. We suggest that climate instability in the early part of the last interglacial may have delayed the melting of the Saalean ice sheets in America and Eurasia, perhaps accounting for this discrepancy.

Evidence for general instability of past climate from a 250-kyr ice-core record

The leading empirical orthogonal function of the wintertime sea-level pressure field is more strongly coupled to surface air temperature fluctuations over the Eurasian continent than the North Atlantic Oscillation (NAO). It resembles the NAO in many respects; but its primary center of action covers more of the Arctic, giving it a more zonally symmetric appearance. Coupled to strong fluctuations at the 50-hPa level on the intraseasonal, interannual, and interdecadal time scales, this "Arctic Oscillation" (AO)can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft. It is proposed that the zonally asymmetric surface air temperature and mid-tropospheric circulation anomalies observed in association with the AO may be secondary baroclinic features induced by the land-sea contrasts. The same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature, sea-level pressure, and 50-hPa height over the past 30 years: parts of Eurasia have warmed by as much as several K, sea-level pressure over parts of the Arctic has fallen by 4 hPa, and the core of the lower stratospheric polar vortex has cooled by several K. These trends can be interpreted as the development of a systematic bias in one of the atmosphere's dominant, naturally occurring modes of variability.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/98GL00950

The Arctic oscillation signature in the wintertime geopotential height and temperature fields

We analyze several year‐long moored current meter records collected on the midshelf and shelf break of the western Antarctic Peninsula in order to describe the major features of the intraseasonal circulation. An empirical orthogonal function (EOF) analysis of all current meter records in any given year reveals that over 49% of the circulation variance follows a spatially coherent, nearly depth‐invariant anticyclonic cell in the downstream vicinity of Marguerite Trough, qualitatively consistent with flow‐topography interaction with the canyon. An analysis of kinetic energy spectra supports the interpretation that the shelf break current is diverted shoreward at the location of the canyon and generates substantial counterclockwise energy at periods shorter than ~10 days as the flow is compressed by a downstream bank. The circulation is well correlated with the long‐shore wind stress both local and remote. Composite velocity profiles under upwelling and downwelling winds show that the change in the barotropic current under different wind states is comparable to or larger than the shear of themean profile in all years. The barotropic velocity fluctuations are generally not coherent with subpycnocline heat content. Plain Language Summary Owing to scarcity of time series of observations on the western Antarctic Peninsula shelf, it has been difficult to diagnose how the currents below the ocean surface vary on time scales of days to weeks. Here we collect an array of ocean velocity measurements from several point locations across and along the shelf at various depths and study the properties of the currents at each site and how the currents at the different sites covary with each other. We find that over half of the circulation variance is nearly depth independent and is spatially coherent over a scale of several hundred kilometers. The circulation's spatial variability is related to the ocean bathymetry, and its temporal variability is related to the winds, both local and far away.

Spatially Coherent Intraseasonal Velocity Fluctuations on the Western Antarctic Peninsula Shelf

We examine the spatiotemporal variability of the upper ocean sea ice system of the Atlantic sector of the Southern Ocean subpolar seas (Weddell gyre) and the nature of its covariability with extrapolar climate. To systematically evaluate the sporadic and sparse distribution of subpolar data, we employed an optimal analysis involving empirical orthogonal functions (EOFs). The EOFs reveal that the pattern of spatial covariability of Weddell gyre characteristics is dominated by high interannual variability near the northern (circumpolar) rim of the gyre and lesser variability (10-20% of the variance) in the gyre's central core region. We find considerable, statistically significant teleconnections between subpolar and extrapolar climate. The dominant link is with El Nino-Southern Oscillation. Our analysis of the gyre characteristics suggest that during El Nino, the Atlantic subpolar (Weddell) gyre spins up while the eastern Pacific subpolar gyre spins down; the opposite occurs for La Nina. This regional subpolar response is consistent with recent GCM modeling analyses. These show that equatorial warm anomalies drive changes in the meridional and zonal atmospheric circulation cells. This results in opposite shifts of the subpolar jets in the Pacific and Atlantic oceans that lead to a change in the interaction (especially in cyclones) between the subtropical and polar front jets in those basins, and ultimately in the cyclonic forcing of the subpolar gyres. We also find that the Weddell gyre interior upper ocean characteristics covary positively with sea ice extent in the Atlantic region and negatively with the sea ice extent in the Amundsen/Bellingshausen regions, reflecting a strong Antarctic dipole.

Spatial/temporal patterns in Weddell gyre characteristics and their relationship to global climate : Southern ocean large-scale variability

Reply [to “Comments on ‘An inverse approach to signal correlation’ by D. G. Martinson, W. Menke, and P. Stoffa”]

Recent observations reveal a signicant change in the upper ocean characteristics of the eastern Arctic in 1995. The change is manifested through the loss of a near-surface layer known as the cold halocline layer (CHL). Without the CHL, the Arctic water column looks and be- haves like the Antarctic water column. The expected local impact is the appearance of signicant winter ocean heat fluxes (15 20 W=m 2 ) and reduction of winter ice growth by70 80% relativetoyearsinwhichtheCHLwaspresent. Preliminary results suggest a partial recovery of theCHL in the late 1990's, tracking the weakening of the Arctic Oscil- lation.

Douglas G. Martinson

Papers

Spatially Coherent Intraseasonal Velocity Fluctuations on the Western Antarctic Peninsula Shelf

Spatial/temporal patterns in Weddell gyre characteristics and their relationship to global climate : Southern ocean large-scale variability

Reply [to “Comments on ‘An inverse approach to signal correlation’ by D. G. Martinson, W. Menke, and P. Stoffa”]

Future of the Arctic Sea Ice Cover: Implications of an

Stable isotope record, calcium carbonate conentrations, and sea surface temperture reconstructions of sediment cores from the North Atlantic