(Table 1) White ice and melt pond characteristics in Darnley and Franklin Bay, Canada

Melt pond covered sea ice is a ubiquitous feature of the summertime Arctic Ocean when meltwater collects in lower-lying areas of ice surfaces. Horizontal transects were conducted during June 2008 above and below landfast sea ice with melt ponds to characterize surface and bottom topography together with variations in transmitted spectral irradiance. We captured a rapid progression from a highly flooded sea ice surface with lateral drainage toward flaws and seal breathing holes to the formation of distinct melt ponds with steep edges. As the mass of the ice cover decreased due to meltwater drainage and rose upward with respect to the seawater level, the high-scattering properties of ice above the water level (i.e., white ice) were continuously regenerated, while pond waters remained transparent compared to underlying ice. The relatively stable albedos observed throughout the study, even as ice thickness decreased, were directly related to these surface processes. Transmission through the ice cover of incident irradiance in the 400-700 nm wave band ranged from 38% to 67% and from 5% to 16% beneath ponded and white ice, respectively. Our results show that this transmission varied not only as a function of surface type (melt ponds or white ice) areal coverage but also in relation to ice thickness and proximity to other surface types through the influence of horizontal spreading of light. Thus, in contrast to albedo, this implies that regional transmittance estimates need to consider melt pond size and shape distributions and variations in optical properties and thickness of the ice cover.

(Table 1) Summary of accelerator mass spectrometer (AMS) radiocarbon ages in ODP Sites 169-1033 and 169-1034

Continuous coring in Saanich Inlet (Ocean Drilling Program, ODP Leg 169S), British Columbia, Canada, yielded a detailed record of Late Quaternary climate, oceanography, marine productivity, and terrestrial vegetation. Two sites (1033 and 1034) were drilled to maximum depths of 105 and 118 m, recovering sediments ranging in age from 13,300 to less than 300 14C yr. Earliest sediments consist of dense, largely massive, gray glaciomarine muds with dropstones and sand and silt laminae deposited during the waning stages of glaciation. Deposition of organic-rich olive gray sediments began in the fjord about 12,000 14C yr ago, under well-oxygenated conditions as reflected by the presence of bioturbation and a diverse infaunal bivalve community. At about 10,500 14C yr, a massive, gray unit, 40-50 cm thick, was emplaced in a very short span of time. The unit is marked by a sharp lower contact, a gradational upper contact and an abundance of reworked Tertiary microfossils. It has been interpreted as resulting from massive flood events caused by the collapse of glacial dams in the Fraser Valley of mainland British Columbia. Progressively greater anoxia in bottom waters of Saanich Inlet began about 7000 14C yr ago. This is reflected in the preservation of varved sediments consisting of diatomaceous spring-summer laminae and terrigenous winter laminae. Correlation of the sediments was based on: marked lithologic changes, the presence of massive intervals (reflecting localized sediment gravity flow events), the Mazama Ash, occasional thin gray laminae (indicative of abnormal flood events in nearby watersheds), varve counts between marker horizons, and 71 accelerator mass spectrometry (AMS) radiocarbon dates.

Distribution of planktonic foraminifera in Pleistocene sediments of the New Jersey margin, NW Atlantic Ocean

Abundance records of planktonic foraminifera (>150 µm) from the upper 520 m of ODP Site 1073 (Hole 1073A, Leg 174A, 639 m water depth) have been integrated with SPECMAP-derived isotope stratigraphy, percentage of calcium carbonate, and coarse sediment fraction data in order to investigate the Pleistocene climatic history of the New Jersey margin. Six planktonic taxonomic groups dominate the foraminiferal assemblage at Site 1073: Neogloboquadrina pachyderma (d) (mean 33.8%), Turborotalita quinqueloba (18.5%), N. pachyderma (s) (18.4%), Globigerina bulloides group (11.4%), Globorotalia inflata group (9.4%), and Globigerinita glutinata (4.1%). Based on the distributions of these six foraminiferal groups, the Pleistocene section can be divided into three paleoclimatic intervals: Interval I (intermediate) corresponds to the Quaternary sediments from sequence boundary pp1 to the seafloor (79.5-0 mbsf; Emiliania huxleyi acme [85 ka] at 72 mbsf); Interval II (warm) occurs between sequence boundaries pp3 and pp1 (325-79.5 mbsf; last occurrence of Pseudoemiliania lacunosa [460 ka] at 330 mbsf); and Interval III (coldest) occurs between sequence boundaries pp4 and pp3 (520-325 mbsf; Calcareous nannofossils and dinocysts in proximity to pp4 indicate that the sedimentary record for 0.9-1.7 Ma is either missing altogether or highly condensed within the basal few meters of the section). Neogloboquadrina pachyderma (d) displays eight peaks of abundance which correlate, for the most part, with depleted delta18O values, increases in calcium carbonate percentages, low coarse fraction percentages, increased planktonic fragmentation (greater dissolution), and low N. pachyderma (s) abundances. These intervals are interpreted as representing warmer/interglacial conditions. Neogloboquadrina pachyderma (s) displays seven peaks of abundance which correlate, for the most part, with delta18O increases, decreases in calcium carbonate percentages, increases in coarse fraction percentages, and low N. pachyderma (d) abundances. These intervals are interpreted as representing cooler/glacial conditions. In Interval III, a faunal response to relative changes in sea-surface temperature is reflected by abundance peaks in Neogloboquadrina pachyderma (d), followed by Turborotalita quinqueloba and then N. pachyderma (s) (proceeding from warmest to coolest, respectively). This tripartite response is consistent with the oxygen isotope record and, although not as clear, also occurs in Intervals I and II. Six peaks/peak intervals of Globigerina bulloides abundance are closely matched by peaks in Globigerinita glutinata and occur within oxygen isotope stage (OIS) 2 (latter part) 3, 4, 5, 8, 9, 13(?), 14(?), and 15(?). We speculate that these intervals reflect increased upwelling and nutrient levels during both glacials and interglacials. Eight peak intervals of Globorotalia inflata show a general inverse correlation with G. bulloides and may reflect lowered nutrient and warmer surface waters.

Age determination of equatorial Pacific sediments

Radiocarbon age differences for pairs of coexisting late glacial age benthic and planktic foraminifera shells handpicked from 10 sediment samples from a core from a depth of 2.8 km in the western equatorial Pacific are not significantly different from that of 1600 years calculated from measurements on prenuclear seawater. This places a lower limit on the depth of the interface for the hypothetical radiocarbon-depleted glacial age seawater reservoir required to explain the 190 per mil drop in the 14C/C for atmospheric CO2, which occurred during the mystery interval (17.5 to 14.5 calendar years ago). These measurements restrict the volume of this reservoir to be no more than 35% that of the ocean. Further, 14C measurements on a single Last Glacial Maximum age sample from a central equatorial Pacific core from a depth of 4.4 km water fail to reveal evidence for the required 5- to 7-kyr age difference between benthic and planktic foraminifera shells if the isolated reservoir occupied only one third of the ocean. Nor does the 13C record for benthic forams from this abyssal core yield any evidence for the excess respiration CO2 expected to be produced during thousands of years of isolation. Nor, as indicated by the presence of benthic foraminifera, was the dissolved oxygen used up in this abyssal water.

Age model and color measurements of sediment cores from the eastern equatorial Pacific

High-resolution records of glacial-interglacial variations in biogenic carbonate, opal, and detritus (derived from non-destructive core log measurements of density, P-wave velocity and color; r >= 0.9) from 15 sediment sites in the eastern equatorial (sampling resolution is ~1 kyr) clear response to eccentricity and precession forcing. For the Peru Basin, we generate a high-resolution (21 kyr increment) orbitally-based chronology for the last 1.3 Ma. Spectral analysis indicates that the 100 kyr cycle became dominant at roughly 1.2 Ma, 200-300 kyr earlier than reported for other paleoclimatic records. The response to orbital forcing is weaker since the Mid-Brunhes Dissolution Event (at 400 ka). A west-east reconstruction of biogenic sedimentation in the Peru Basin (four cores; 91-85°W) distinguishes equatorial and coastal upwelling systems in the western and eastern sites, respectively. A north-south reconstruction perpendicular to the equatorial upwelling system (11 cores, 11°N-°3S) shows high carbonate contents (>= 50%) between 6°N and 4°S and highly variable opal contents between 2°N and 4°S. Carbonate cycles B-6, B-8, B-10, B-12, B-14, M-2, and M-6 are well developed with B-10 (430 ka) as the most prominent cycle. Carbonate highs during glacials and glacial-interglacial transitions extended up to 400 km north and south compared to interglacial or interglacial^glacial carbonate lows. Our reconstruction thus favors glacial-interglacial expansion and contraction of the equatorial upwelling system rather than shifting north or south. Elevated accumulation rates are documented near the equator from 6°N to 4°S and from 2°N to 4°S for carbonate and opal, respectively. Accumulation rates are higher during glacials and glacial-interglacial transitions in all cores, whereas increased dissolution is concentrated on Peru Basin sediments close to the carbonate compensation depth and occurred during interglacials or interglacial-glacial transitions.