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Geology topics

Harry J. Dowsett

Publications and source records attributed to Harry J. Dowsett.

At least 73 records · Page 4Linked to original sources
USGS2010

Mid-Piacensian mean annual sea surface temperature: an analysis for data-model comparisons

Numerical models of the global climate system are the primary tools used to understand and project climate disruptions in the form of future global warming. The Pliocene has been identified as the closest, albeit imperfect, analog to climate conditions expected for the end of this century, making an independent data set of Pliocene conditions necessary for ground truthing model results. Because most climate model output is produced in the form ofmean annual conditions, we present a derivative of the USGS PRISM3 Global Climate Reconstruction which integrates multiple proxies of sea surface temperature (SST) into single surface temperature anomalies. We analyze temperature estimates from faunal and floral assemblage data,Mg/Ca values and alkenone unsaturation indices to arrive at a single mean annual SST anomaly (Pliocene minus modern) best describing each PRISM site, understanding that multiple proxies should not necessarily show concordance. The power of themultiple proxy approach lies within its diversity, as no two proxies measure the same environmental variable. This data set can be used to verify climate model output, to serve as a starting point for model inter-comparisons, and for quantifying uncertainty in Pliocene model prediction in perturbed physics ensembles.

Stratigraphy↗
USGS2010

Climate change lessons from a warm world

In the early 1970’s to early 1980’s Soviet climatologists were making comparisons to past intervals of warmth in the geologic record and suggesting that these intervals could be possible analogs for 21st century “greenhouse” conditions. Some saw regional warming as a benefit to the Soviet Union and made comments along the lines of “Set fire to the coal mines!” These sentiments were alarming to some, and the United States Geological Survey (USGS) leadership thought they could provide a more quantitative analysis of the data the Soviets were using for the most recent of these warm intervals, the Early Pliocene.

Transactions of the Leicester Literary & Philosoph↗
USGS2009

Impact of a permanent El Niño (El Padre) and Indian Ocean Dipole in warm Pliocene climates

Pliocene sea surface temperature data, as well as terrestrial precipitation and temperature proxies, indicate warmer than modern conditions in the eastern equatorial Pacific and imply permanent El Niño–like conditions with impacts similar to those of the 1997/1998 El Niño event. Here we use a general circulation model to examine the global-scale effects that result from imposing warm tropical sea surface temperature (SST) anomalies in both modern and Pliocene simulations. Observed SSTs from the 1997/1998 El Niño event were used for the anomalies and incorporate Pacific warming as well as a prominent Indian Ocean Dipole event. Both the permanent El Niño (also called El Padre) and Indian Ocean Dipole (IOD) conditions are necessary to reproduce temperature and precipitation patterns consistent with the global distribution of Pliocene proxy data. These patterns may result from the poleward propagation of planetary waves from the strong convection centers associated with the El Niño and IOD.

Paleoceanography↗
USGS2009

PRISM3/GISS Topographic Reconstruction

The PRISM3/GISS topographic reconstruction is one of the global data sets incorporated into a new reconstruction for the mid-Piacenzian warm interval of the Pliocene, at about 3.3 to 3.0 Ma. The PRISM3/GISS topography-gridded data set is a digitization of a graphical reconstruction, provided at 2 deg x 2 deg resolution and based on updated paleoaltimetry data and a refined land/ocean mask. Mid-Piacenzian topography as shown in this data set is generally quite similar to modern topography, with three notable differences: (1) the coastline as shown is 25 meters higher than modern sea level, reflecting the hypothesized reduction in ice sheet volume; (2) Hudson Bay is filled in to low elevation, in the absence of evidence for submergence at that time; and (3) the West Antarctic ice sheet is absent, permitting open seaways to exist in Ellsworth and Marie Byrd Lands. Two alternate ice sheet configurations with corresponding vegetation schemes are available; one is a minor modification of the PRISM2 ice reconstruction, and one is derived from the British Antarctic Survey Ice Sheet Model (BAS ISM).

Data Series↗
USGS2008

Mid-Pliocene equatorial Pacific sea surface temperature reconstruction: a multi-proxy perspective

The Mid-Pliocene is the most recent interval of sustained global warmth, which can be used to examine conditions predicted for the near future. An accurate spatial representation of the low-latitude Mid-Pliocene Pacific surface ocean is necessary to understand past climate change in the light of forecasts of future change. Mid-Pliocene sea surface temperature (SST) anomalies show a strong contrast between the western equatorial Pacific (WEP) and eastern equatorial Pacific (EEP) regardless of proxy (faunal, alkenone and Mg/Ca). All WEP sites show small differences from modern mean annual temperature, but all EEP sites show significant positive deviation from present-day temperatures by as much as 4.4°C. Our reconstruction reflects SSTs similar to modern in the WEP, warmer than modern in the EEP and eastward extension of the WEP warm pool. The east-west equatorial Pacific SST gradient is decreased, but the pole to equator gradient does not change appreciably. We find it improbable that increased greenhouse gases (GHG) alone would cause such a heterogeneous warming and more likely that the cause of Mid-Pliocene warmth is a combination of several forcings including both increased meridional heat transport and increased GHG.

Philosophical Transactions of the Royal Society A:↗
USGS2008

Surface temperatures of the Mid-Pliocene North Atlantic Ocean: Implications for future climate

The Mid-Pliocene is the most recent interval in the Earth's history to have experienced warming of the magnitude predicted for the second half of the twenty-first century and is, therefore, a possible analogue for future climate conditions. With continents basically in their current positions and atmospheric CO 2 similar to early twenty-first century values, the cause of Mid-Pliocene warmth remains elusive. Understanding the behaviour of the North Atlantic Ocean during the Mid-Pliocene is integral to evaluating future climate scenarios owing to its role in deep water formation and its sensitivity to climate change. Under the framework of the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) sea surface reconstruction, we synthesize Mid-Pliocene North Atlantic studies by PRISM members and others, describing each region of the North Atlantic in terms of palaeoceanography. We then relate Mid-Pliocene sea surface conditions to expectations of future warming. The results of the data and climate model comparisons suggest that the North Atlantic is more sensitive to climate change than is suggested by climate model simulations, raising the concern that estimates of future climate change are conservative.

Philosophical Transactions of the Royal Society A:↗
USGS2008

Reevaluation of mid-Pliocene North Atlantic sea surface temperatures

Multiproxy temperature estimation requires careful attention to biological, chemical, physical, temporal, and calibration differences of each proxy and paleothermometry method. We evaluated mid-Pliocene sea surface temperature (SST) estimates from multiple proxies at Deep Sea Drilling Project Holes 552A, 609B, 607, and 606, transecting the North Atlantic Drift. SST estimates derived from faunal assemblages, foraminifer Mg/Ca, and alkenone unsaturation indices showed strong agreement at Holes 552A, 607, and 606 once differences in calibration, depth, and seasonality were addressed. Abundant extinct species and/or an unrecognized productivity signal in the faunal assemblage at Hole 609B resulted in exaggerated faunal-based SST estimates but did not affect alkenone-derived or Mg/Ca–derived estimates. Multiproxy mid-Pliocene North Atlantic SST estimates corroborate previous studies documenting high-latitude mid-Pliocene warmth and refine previous faunal-based estimates affected by environmental factors other than temperature. Multiproxy investigations will aid SST estimation in high-latitude areas sensitive to climate change and currently underrepresented in SST reconstructions.

Paleoceanography↗
USGS2001

Variations in river flow to the Gulf of Mexico: implications for paleoenvironmental studies of Gulf of Mexico marine sediments

Analyses of selected gaging station records from the Mississippi River and Rio Grande show that variations in discharge of these rivers into the Gulf of Mexico reflect major flood events and regional-scale drought intervals known from the historical record. Variations in Rio Grande discharge show good correlation with El Ni?o/Southern Oscillation (ENSO) events and short-term variability. Mississippi River discharge does not show correlation with ENSO events or short-term variability. However, Mississippi River discharge does appear to respond to long-term changes in ENSO variability and mean climate state. The link between historical hydrologic extremes and discharge of the Rio Grande and Mississippi River into the Gulf of Mexico indicates that shelf and slope sediments of the Gulf of Mexico contain a long-term record of flood and drought intervals of the Southwestern and Central United States.

Bulletin↗
USGS2000

Data report: Pliocene planktonic foraminifers from the California margin: Site 1021

This report is an initial investigation of the planktonic foraminifers from the late Pliocene of Ocean Drilling Program Hole 1021C. Planktonic foraminifer assemblages show fair preservation in many samples. Assemblages are quantitatively dominated by Globigerina bulloides, dextral coiling Neogloboquadrina atlantica, and Globorotalia inflata and alternate between cool temperate and subarctic conditions.

California↗
USGS1999

Last interglacial sea-surface temperature estimates from the California margin; improvements to the modern analog technique

Total faunal analyses of planktic foraminifer assemblages are used to derive sea surface temperature estimates for the last interglacial from Ocean Drilling Program Sites 1018 and 1020 off northern and central California. Foraminifer assemblage data were transformed to sea-surface temperature (SST) estimates by using the modern analog technique (MAT). In order to improve our ability to estimate SST in this area, the coretop calibration data base used in the MAT was augmented by 13 new age-validated coretop assemblages from the U.S. Pacific Margin.

Bulletin↗
USGS1999

Sediment color and reflectance record from Ocean Drilling Program Hole 625B, Gulf of Mexico (marine isotope stage 5 interval)

Analysis of climate indicators from the North Atlantic, California Margin, and ice cores from Greenland suggest millennial scale climate variability is a component of earth's climate system during the last interglacial period (marine oxygen isotope stage 5). The USGS is involved in a survey of high resolution marine records covering the last interglacial period (MIS 5) to further document the variability of climate and assess the rate at which climate can change during warm intervals. The Gulf of Mexico (GOM) is an attractive area for analysis of climate variability and rapid change. Changes in the Mississippi River Basin presumably are translated to the GOM via the river and its effect on sediment distribution and type. Likewise, the summer monsoon in the southwestern US is driven by strong southerly winds. These winds may produce upwelling in the GOM which will be recorded in the sedimentary record. Several areas of high accumulation rate have been identified in the GOM. Ocean Drilling Program (ODP) Site 625 appears to meet the criteria of having a well preserved carbonate record and accumulation rate capable of discerning millennial scale changes.

Open-File Report↗
USGS1997

Application of the Modern Analog Technique (MAT) of sea surface temperature estimation to middle Pliocene North Pacific planktonic foraminifer assemblages

Seventy-two samples from Deep Sea Drilling Project Sites 445 and 463 and Ocean Drilling Program Site 769 from the northwest Pacific Ocean were compared to 499 modern core top Pacific Ocean samples using the squared chord distance dissimilarity measure. Many samples show high levels of dissimilarity that can be explained by pervasive dissolution and/or evolution changing the composition of the fossil assemblages. Weighted averages of winter and summer sea surface temperatures (SST) from the nearest five modern analogs of each fossil-bearing sample were used to estimate Pliocene SST. Results show little to no middle Pliocene warming at low latitudes (Site 769) and warming of 2°C to 4°C in winter and possibly 1°C in summer just north of the Philippine Sea (Site 445). These data, when combined with other estimates of Pliocene SST in the northwest Pacific, suggest an enhanced meridional oceanic heat flow, similar to that found in the North Atlantic during the same part of the Pliocene.

Palaeontologia Electronica↗