Terrestrial chronologies from southern Greenland provide a detailed deglacial history of the Greenland Ice Sheet (GIS). The northern GIS margin history, however, is less established. Here we present surface exposure ages from moraines associated with two large outlet glaciers, Petermann and Humboldt, in the northwestern sector of the GIS. These...
Study of the eolian fraction of late Quaternary sediments from the tropical Atlantic reveals that two modes of long-term climate variability have existed in tropical Africa during the last 150,000 yr. Tropical northwest Africa (i.e., the southwestern Sahara and Sahel) was driest during glaciations and stades, but wetter than at...
Most of the policy debate surrounding the actions needed to mitigate and adapt to anthropogenic climate change has been framed by observations of the past 150 years as well as climate and sea-level projections for the twenty-first century. The focus on this 250-year window, however, obscures some of the most...
We use flux, dissolution, and excess ²³⁰Th data from the Joint Global Ocean Flux Study and Manganese Nodule Project equatorial Pacific study Site C to assess the extent of sediment focusing in the equatorial Pacific. Measured mass accumulation rates (MAR) from sediment cores were compared to reconstructed MAR by multiplying...
Sea surface temperatures (SST) and inorganic continental input over the last 25,000 years (25 ka) are reconstructed in the far eastern equatorial Pacific (EEP) based on three cores stretching from the equatorial front (~0.01°N, ME0005-24JC) into the cold tongue region (~3.6°S; TR163-31P and V19-30). We revisit previously published alkenone-derived SST...
Deciphering the evolution of global climate from the end of the Last Glacial Maximum approximately 19 ka to the early Holocene 11 ka presents an outstanding opportunity for understanding the transient response of Earth's climate system to external and internal forcings. During this interval of global warming, the decay of...
Biogenic opal, organic carbon, organic matter stable isotope, and trace metal data from
a well-dated, high-resolution jumbo piston core (EW0408–85JC; 59° 33.3′N, 144° 9.21′W,
682 m water depth) recovered from the northern Gulf of Alaska continental slope reveal
changes in productivity and nutrient utilization over the last 17,000 years. Maximum...
Assessing impacts of future anthropogenic carbon emissions is currently impeded by uncertainties in our knowledge of equilibrium climate sensitivity to atmospheric carbon dioxide doubling. Previous studies suggest 3 K as best estimate, 2–4.5 K as the 66% probability range, and non-zero probabilities for much higher values, the latter implying a...
We present a new nitrogen isotope model incorporated into the three-dimensional ocean component of a global Earth system climate model designed for millennial timescale simulations. The model includes prognostic tracers for the two stable nitrogen isotopes, 14N and 15N, in the nitrate (NO3−), phytoplankton, zooplankton, and detritus variables of the...
We examine the relation between δ¹⁸O in rainwater collected in southwestern Oregon
and climate variables including temperature, parcel trajectory, precipitation amount, and
specific humidity. Local surface air temperature at the time of sample collection explains a
large proportion of δ¹⁸O variability, suggesting that paleoclimatic archives that are related
to rainfall...
The Penman‐Monteith equation is often used to estimate transpiration, but an important limitation to this approach, especially for mountainous forested sites, is an accurate estimate of canopy conductance averaged over the area of interest (Gs). We propose a method for estimating watershed‐scale transpiration using estimates of Gs derived from measurements...
Here we present the first downcore results for a new paleoproxy, the Mn/Ca ratio of foraminiferal calcite, applied to sediment accumulated in the extreme Eastern Tropical North Pacific (ETNP) over the last 30,000 years. The Mn/Ca results are compared to oxygen isotopes and sea surface temperature calculated from Mg/Ca. We...
Application of the ²³⁰Th normalization method to estimate sediment burial fluxes in six cores from the
eastern equatorial Pacific (EEP) reveals that bulk sediment and organic carbon fluxes display a coherent regional
pattern during the Holocene that is consistent with modern oceanographic conditions, in contrast with estimates
of bulk mass...
Ocean Drilling Program (ODP) Leg 202 has opened a new window
into understanding late Paleogene and Neogene global environmental
change by providing high-quality sediment sequences from a previously
unsampled region, the eastern South Pacific. Eleven sites (1232–
1242) that record variations on timescales ranging from decades to tens
of millions...
Sea surface temperature (SST) and salinity of the Western Pacific Warm Pool (WPWP) reflect global climate effects such as the El Niño–Southern Oscillation phenomenon. However, reconstructions of past changes in the WPWP from the geologic record vary depending on the specific proxy record used. Here we develop a multiproxy record...
Multiproxy geologic records of δ18O and Mg/Ca in fossil foraminifera from sediments under the Eastern Pacific Warm Pool (EPWP) region west of Central America document variations in upper ocean temperature, pycnocline strength, and salinity (i.e., net precipitation) over the past 30 kyr. Although evident in the paleotemperature record, there is...
The primary Mg/Ca ratio of foraminiferal shells is a potentially valuable paleoproxy for sea surface
temperature (SST) reconstructions. However, the reliable extraction of this ratio from sedimentary calcite
assumes that we can overcome artifacts related to foraminiferal ecology and partial dissolution, as well as
contamination by secondary calcite and clay....
The mass accumulation rates of sedimentary components (carbonate, organic carbon, opal, barite, reactive phosphate, iron, terrigenous minerals, etc.) are used in many paleoceanographic reconstructions to learn about temporal and spatial changes in surficial Earth processes including wind stress and direction, oceanic circulation, weathering rates, marine productivity and ecosystem structure, climate...
The isotopic composition of the dissolved inorganic carbon (DIC) collected at sites of active methane discharge on Hydrate Ridge, Oregon, reveals anaerobic methane oxidation mediated by bacteria, with δ13CDIC reaching values as low as –48‰ in the upper 4 cm of the sediment. In spite of the high sulfide levels...
Mg/Ca ratios in planktonic foraminifera reflect calcification temperatures and are thus useful for sea
surface temperature (SST) reconstructions. Despite the obvious utility of this paleoceanographic tracer,
problems of dissolution, gametogenic calcification, and contaminant phases have thus far limited
confidence in Mg/Ca-based reconstructions. Here we show strong evidence of Mg heterogeneity...