The NSF and the geosciences community: Rotating program officers

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95447/1/eost7407.pd

Aspects of atmospheric circulation: the late Pleistocene (0-950,000 yr) record of eolian deposition in the pacific ocean

The eolian component of pelagic sediments provides a proxy record of atmospheric circulation intensity and of dust transport. Examination of those records indicates that the atmosphere responds to orbital forcing but that during the past 875,000 years the, variability in atmospheric circulation is at much shorter periods than the 100,000-year variation in ice volume. The mid-Brunhes climatic event is well characterized in the eolian grain-size records and in records of sea-surface phenomena; it is not seen in proxy indicators of either deep-water or ice-volume variability. The increase in the amplitude of paeloclimatic variability that denotes the early/late Pleistocene transition occurs suddenly about 875,000 years ago in the eolian grain-size record, which is about 20,000 to 25,000 years earlier than the transition in the deep sea CaCO3-dissolution record or in the [delta]18O proxy record of ice volume.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28534/1/0000332.pd

Analysis of a fast-spreading rise crest: The East Pacific Rise, 9° to 12° south

The axis of the East Pacific Rise is defined by a topographic block about 15 km wide and 300 to 350 m high which is flanked by abyssal hills 100 to 200 m high and 3 to 5 km wide. These hills often are tilted such that their steep slopes face the axis. An empirical model explaining these features combines axial extrusion to form the central block and rotational faulting to lower the shoulders of the axial block to the regional depth and tilt them outward.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43191/1/11001_2004_Article_BF00426250.pd

Late Tertiary history of hydrothermal deposition at the East Pacific Rise, 19°S: Correlation to volcano‐tectonic events

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95132/1/grl3614.pd

Neogene history of the south Pacific tradewinds: Evidence for hemispherical asymmetry of atmospheric circulation

Eolian dust grains extracted from southeast Pacific pelagic sediments provide a Neogene record of southern hemisphere atmospheric processes. The mass accumulation rate of dust has been low and generally constant at 1-4 mg/cm2 103 y since the late Oligocene. Eolian grainsize data show an increase from 8.2[phi] (3.40 [mu]) in older sediments to 7.2[phi] (6.8o [mu]) in younger material. This shift occurred about 10.5 m.y. ago and reflects a significant increase in the intensity of atmospheric circulation then. There is no obvious response to the onset of northern hemisphere glaciation 2.5 m.y. ago in these eolian records from the South Pacific. Comparison with existing information from the northern hemisphere suggests that the southern hemisphere has had more intense atmospheric circulation throughout the Neogene and that this asymmetry reached its greatest extent between 10.5 and 2.5 Ma.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26165/1/0000242.pd

Eastern Pacific spreading rate fluctuation and its relation to Pacific area volcanic episodes

Sea-floor spreading rates from four locations along the Nazca-Pacific plate boundary and one along the Juan de Fuca-Pacific plate boundary show variations over the past 2.4 m.y., with decreasing rates prior to the Jaramillo to Olduvai time interval (0.92-1.73 m.y. ago) and increasing rates since then. Other Pacific area volcanic phenomena in mid-plate and convergent-boundary settings also show minima about 1.3-1.5 m.y. ago and a maximum at present and another maximum about 5 m.y. ago: extrusion rates along the Hawaiian Ridge; volcanic episodes associated with calc-alkalic provinces of western Oregon and Central America; temporal variations in the SiO2 content of Aleutian ash layers; and the number of deep-sea ash layers. These phenomena may fluctuate in response to changing spreading rates. During times of more rapid spreading increased shear and melting along lithospheric boundaries may occasion increased volcanic activity, whereas during times of less rapid spreading volcanic activity may be less intense.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23637/1/0000601.pd

Dry bulk density and CaCO3 relationships in upper Quaternary sediments of the eastern equatorial Pacific

Results from 1110 paired CaCO3 and bulk density measurements from cores raised from the eastern equatorial Pacific permit formulation of well constrained CaCO3-DBD relationships for that region. The cores lie along a N-S transect at 110[deg]W from 10[deg]N to 3[deg]S underneath the different currents of the equatorial current system and along an E-W transect from 110[deg] to 90[deg]W, at approximately 3[deg]S. Two distinct, crescent-shaped dry bulk density-CaCO3 relationships are observed. For equal CaCO3 percentages, sediments from those sites at 110[deg]W, which are situated in the high productivity zone, have lower dry bulk density. Cores raised from closer to shore have relatively greater DBD.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31363/1/0000275.pd

Late Cenozoic changes in atmospheric circulation deduced from North Pacific eolian sediments

Isolation and analysis of the eolian component of late Cenozoic pelagic sediments from the North Pacific provides direct information concerning changes in atmospheric circulation. A 50% increase in intensity of both the prevailing westerlies and the tradewinds coincides with increasing pole-to-equator temperature gradients resulting from the onset of northern hemisphere glaciation. At the same time, the mass flux of dust from continents to the North Pacific increased by a factor of 4.5, apparently reflecting significantly increased continental aridity associated with the late Cenozoic glacial ages.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23873/1/0000112.pd

Quaternary fluctuations in the Northern Hemisphere trade winds and westerlies

The mass accumulation rate and grain size of the total colian component isolated from pelagic sediment in two North Pacific cores, piston core KK75-02 under the prevailing westerlies and Deep-Sea Drilling Project Site 503 beneath the trade winds, have been used to evaluate changes in the intensity of atmospheric circulation and source-area aridity over the past 700,000 yr. The eolian grain size, a direct indicator of wind intensity, fluctuates at periodicities similar to those calculated for the earth's orbital parameters of precession, obliquity, and eccentricity. Both sites display greater variability in wind intensity prior to 250,000 yr ago. Eolian accumulation rates, an indicator of source-area aridity, fluctuate at periodicities similar to those of the glacial-interglacial cycles. Lower eolian accumulation rates during colder (glacial) times most likely reflect increased glacial-age humidity at central Asian and Central American source areas.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25580/1/0000124.pd

Volcanic activity and global change: probable short-term and possible long-term linkages

Article reviews annual to decadal climate response to volcanism; long-term climatic response to volcanism; and recent results from ocean drilling in the North Pacific