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Growing evidence suggests that the low atmospheric C[O.sub.2] concentration of the ice ages resulted from enhanced storage of C[O.sub.2] in the ocean interior, largely as a result of changes in [...]

Air bubbles trapped in Antarctic ice reveal that the atmospheric concentration of carbon dioxide (C[O.sub.2]) has varied over ice age cycles, between 280 parts per million by volume (ppmv) during [...], Since the first evidence of low algal productivity during ice ages in the Antarctic Zone of the Southern Ocean was discovered, there has been debate as to whether it was associated with increased polar ocean stratification or with sea-ice cover, shortening the productive season. The sediment concentration of biogenic barium at Ocean Drilling Program site 882 indicates low algal productivity during ice ages in the Subarctic North Pacific as well. Site 882 is located southeast of the summer sea-ice extent even during glacial maxima, ruling out sea-ice-driven light limitation and supporting stratification as the explanation, with implications for the glacial cycles of atmospheric carbon dioxide concentration.

There is increasing evidence that the preceding Holocene climate was as unstable as the last glacial period, although variations occurred at much lower amplitudes. However, low-latitude climate records that confirm this variability are sparse. Here we present a radiocarbon-dated Holocene marine record from the tropical western Atlantic. Aragonite dissolution derived from the degree of preservation of the pteropod Limacina inflata records changes in the corrosiveness of the bottom water at the core site due to the changing influence of northern versus southern water masses. The [delta][sup.18]O difference between the shallow-living planktonic foraminifera Globigerinoides sacculifer and the deep-living Globorotalia tumida is used as proxy for changes in the vertical stratification of the surface water, hence the trade wind strength at this latitude. We compared our data to high-latitude records of the North Atlantic region. A good agreement is found between the aragonite dissolution and the strength in the Island-Scotland Overflow Water, which contributes significantly to the North Atlantic Deep Water. This suggests that large-scale variations in the Atlantic thermohaline circulation occurred throughout the Holocene. Concurrently, the comparison of our [DELTA][delta][sup.18]O with the GISP2 glaciochemical records points to global Holocene atmospheric reorganizations seen in both the tropics and high northern latitudes. Keywords: Holocene, tropical Atlantic, oceanography, stable oxygen isotopes, carbonate preservation, thermohaline circulation.

Two recently drilled Caribbean sites contain expanded sedimentary records of the late Paleocene thermal maximum, a dramatic global warming event that occurred at ca. 55 Ma. The records document significant environmental changes, including deep-water oxygen deficiency and a mass extinction of deep-sea fauna, intertwined with evidence for a major episode of explosive volcanism. We postulate that this volcanism initiated a reordering of ocean circulation that resulted in rapid global warming and dramatic changes in the Earth's environment.

The late Paleocene thermal maximum (LPTM) is associated with a brief, but intense, interval of global warming and a massive perturbation of the global carbon cycle. We have developed a new orbital chronology for Ocean Drilling Program (ODP) Site 690 (Weddell Sea, Southern Ocean) by using spectral analysis of high-resolution geochemical records. The LPTM interval spans 11 precessional cycles yielding a duration of 210 to 220 k.y. The [[Delta].sup.13]C anomaly associated with the LPTM has a magnitude of about -2.5% to -3%; we show that about -2% of the excursion occurs within two steps that each were less than 1000 yr in duration. The remainder developed through a series of steps over ~52 k.y. The timing of these steps is consistent with a series of nearly catastrophic releases of methane from gas hydrates, punctuated by intervals of relative equilibria between hydrate dissociation and carbon burial. Further, we are able to correlate the records between ODP Sites 690 and 1051 (western North Atlantic) on the scale of 21 k.y. cycles, which demonstrates that the details of the [[Delta].sup.13]C excursion are recognizable between distant sites. Comparison of cycle records at Sites 690 and 1051 suggests that sediment representing the interval ~30 k.y. just prior to and at the onset of the LPTM are missing in the latter location. This unconformity probably resulted from slope failure accompanying methane hydrate dissociation within 10 k.y. of the start of the LPTM. Keywords: cyclostratigraphy, paleoceanography, global warming, Paleocene, XRF scanner.

Nature 495, 495-498 (2013); doi:10.1038/nature12006 In Figure 3c of our Letter, the time axis of the ln(Si/Al) record of ODP Site 658A (orange line) was based on a prior age [...]