Geochemical composition and granulometry of ODP Hole 167-1017E sediments

Intensification of North Pacific Intermediate Water during the Younger Dryas and stadials of the last glacial episode has been advocated by Kennett and his colleagues based on studies of ventilation history in Santa Barbara Basin. Because Santa Barbara Basin is a semi-isolated marginal basin, this hypothesis requires testing in sequences on the upper continental margin facing the open-ocean of the Pacific. Ocean Drilling Program Site 1017 is located on the upper slope of southern California off Point Conception close to the entrance of Santa Barbara Basin, an ideal location to test the hypothesis of late Quaternary switching in intermediate waters. We examined chemical and mineral composition, sedimentary structures, and grain size of hemipelagic sediments representing the last 80 k.y. at this site to detect changes in behavior of intermediate waters. We describe distinct compositional and textual variations that appear to reflect changes in grain size in response to flow velocity fluctuations of bottom waters. Qualitative estimates of changes in degree of pyritization indicate better ventilation of bottom water during intervals of stronger bottom-water flow. Comparison between variations in the sediment parameters and the planktonic d18O record indicates intensified bottom-current activity during the Younger Dryas and stadials of marine isotope Stage 3. This result strongly supports the hypothesis of Kennett and his colleagues. Our investigation also suggests strong grain-size control on organic carbon content (and to less extent carbonate carbon content). This, in turn, suggests the possibility that organic carbon content of sediments, which is commonly used as an indicator of surface productivity, can be influenced by bottom currents.

Organic geochemistry of sediments at DSDP Leg 63 Holes

Selected core samples from the California Continental Borderland (Sites 467-469) were analyzed to evaluate the nature and composition of the lipids and kerogens in terms of their genetic origin and geological maturity. The lipids were of a multiple origin. On the basis of the homolog distributions of the n-alkanes and n-fatty acids, with the shape and magnitude of the unresolved branched and cyclic hydrocarbons, and the structural and stereochemical compositions of the molecular markers, these lipids were derived from primary autochthonous marine (microbial), from allochthonous terrigenous (higher plant wax), and from recycled (geologically mature organic matter) sources. The kerogens were composed of principally marine microbial detritus with a minor input of allochthonous terrestrial material. For the most part, the samples had undergone a thermal maturation according to a normal geothermal gradient, except in the proximity of intrusives. Such additional thermal stress was evident for the samples from Site 469 and to some extent for Site 467 at about a sub-bottom depth of 700 to 800 meters.

Nd isotopes of ODP Sites 146-893 and 167-1017 samples

Changes in the source of intermediate waters to the southern California margin may have caused variations in seafloor oxygen levels on stadial-interstadial time scales. We test this hypothesis using the Nd isotopic composition of benthic foraminifera and fossil fish debris from ODP Sites 893 and 1017 to track the composition of intermediate waters across interstadials 8-14 (~37-52 ka) during Marine Isotope Stage 3. The epsilon-Nd values of waters bathing the seafloor at Site 893 were typically ~-9 and those bathing Site 1017 were ~-7, both of which are significantly less radiogenic than waters that had originated in either the North Pacific or Southern Ocean (by the time such waters reached the southern California margin). Detrital silicate epsilon-Nd values of nearly -12 suggest that this offset toward lower epsilon-Nd values was likely caused by boundary scavenging that partially overprinted the water mass composition with local/regional fluvial Nd inputs. In spite of the evidence for boundary scavenging, the lack of systematic seawater Nd isotope changes on a stadial-interstadial basis suggests that the provenance of the intermediate waters did not change, and that the waters were derived from the Southern Ocean. Instead, changes in local/regional sea surface productivity may have caused the recorded changes in seafloor oxygenation.

Clay minerals and their assemblages at DSDP Leg 63 Holes

This paper discusses the distribution of clay minerals and identification of their assemblages in relation to sedimentary facies encountered during DSDP Leg 63 drilling off southern California and Baja California. We also consider how these assemblages are determined by source areas and changes in general paleogeographic environments during different periods of sedimentation.

Petrography and mineral compositions of gabbros at DSDP Leg 60 Holes

The compositions, mineralogies, and textures of gabbros recovered in polymict breccias in Hole 453 indicate that they are the cumulus assemblages of calc-alkalic crystal fractional on that occurred beneath the West Mariana Ridge. They are among a class of gabbros known only from other calc-alkalic associations (e.g., the Lesser Antilles and the Peninsular Ranges batholith of Southern California) and differ from gabbros of stratiform complexes, ophiolites, and the ocean crust. Particularly abundant in the Hole 453 breccias are olivine-bearing gabbros with extremely calcic Plagioclase (An94-97) but with fairly iron-rich olivines (Fo76-77). Other gabbros contain biotite and amphibole and occur in breccias with fairly high-grade greenschist facies (amphibole-chlorite-stilpnomelane) metabasalts. One unusual gabbro has experienced almost complete subsolidus recrystallization to an assemblage of aluminous magnesio-hornblende, anorthite, and green hercynitic spinel. This reaction, the extremely calcic Plagioclase, the occurrence of biotite and amphibole, and the association with greenschist facies metamorphic rocks suggest that crystallization of the gabbros occurred at elevated P(H2O). Comparisons with other calc-alkalic gabbro suites suggest pressures in excess of 4 kbar (about 12 km depth). The gabbros were exposed by the early stages of opening of the Mariana Trough and imply that considerable uplift may have attended rifting. They were also subjected to hydrothermal alteration after breccia formation, resulting in formation of chlorite, epidote, actinolite, and prehnite. Temperatures of at least 200°C - and probably 350°C - were reached, and most likely could not have been attained without extrusion or intrusion of magmas nearby, even though no such rocks were cored.

Age determination and stable oxygen isotope record of ODP Hole 167-1017E

Oxygen isotopic (d18O) climatic stratigraphy and radiocarbon chronology, at high resolution, have been used to establish an age model for Ocean Drilling Program Hole 1017E, a continuous 25-m sequence of hemipelagic sediments from the continental slope (956 m water depth), east of Point Arguella, Southern California. The upper part of Hole 1017E from ~33 ka (7.445 mbsf) was dated using 13 calendar-corrected radiocarbon ages of mixed planktonic foraminiferal assemblages. Benthic oxygen isotopic stratigraphy records a continuous 130-k.y. sequence ranging from marine isotope Stage 6 to the present day. The benthic d18O curve, representing the last two interglacial and glacial cycles, closely resembles the well-dated, deep-sea reference sequence, providing a detailed chronologic framework. Sedimentation rates remained relatively constant throughout the sequence at ~18 cm/k.y. and were sufficiently rapid to provide considerable potential for high-resolution paleoceanographic/paleoclimatic investigations. Planktonic foraminiferal oxygen isotopic stratigraphy based on the surface-dwelling form Globigerina bulloides defines an almost complete sequence of interstadial/stadial oscillations (Dansgaard/Oeschger cycles [D/O]). Combined use of radiocarbon chronology, deep-sea oxygen isotopic datums, and visual pattern matching has enabled us to identify the sequence of D/O cycles as described for the Greenland (GRIP2) ice core. This has strengthened the stratigraphic framework for the last 60 k.y. in the sequence as a basis for further paleoenvironmental investigations.

Stable isotope stratigraphy of ODP Site 167-1014

Late Quaternary oxygen (d18O) and carbon (d13C) isotopic records for the benthic foraminifer Uvigerina and the planktonic foraminifer Globigerina bulloides are presented for the upper 20 meters composite depth sediment sequence of Ocean Drilling Program Site 1014, Tanner Basin, in the outer California Borderland province. The benthic oxygen isotopic record documents a continuous >160-k.y. sequence from marine isotope Stage (MIS) 6 to the present day. The record closely resembles other late Quaternary North Pacific benthic isotope records, as well as the well-dated deep-sea sequence (SPECMAP), and thus provides a detailed chronologic framework. Site 1014 provides a useful record of the California response to climate change as it enters the southern California Border-land. Sedimentation rates are relatively constant and high (~11.5 cm/k.y. ). The planktonic foraminiferal record is well pre-served except during marine isotope Substages 5b and 5d, when normally high G. bulloides abundance is strongly diminished as a result of dissolution. The planktonic oxygen isotopic shift of ~3 per mil between the last glacial maximum and the Holocene suggests a surface water temperature shift of <7°C, similar to estimates from Hole 893A (Leg 146) to the north. Unlike Santa Barbara Basin, G. bulloides d18O values during the last interglacial (MIS 5) at Site 1014 were significantly higher than during the Holocene. In particular, marine isotope Substage 5e (Eemian) was ~0.8 per mil higher. This is unlikely to reflect a cooler Eemian but is instead the result of preferential dissolution of thin-shelled (low d18O) specimens during this interval. In this mid-depth basin, a large benthic d18O shift during Termination I suggests dramatic temperature and salinity changes in response to switches in the source of North Pacific Intermediate Water. Although d13C values of the planktonic foraminifer G. bulloides are in disequilibria with seawater and hence interpretations are limited, the G. bulloides record exhibits several negative d13C excursions found at other sites in the region (Sites 1017 and 893). This indicates a response of G. bulloides d13C to regional surface water processes along the southern California margin. A general increase in benthic carbon isotopic values (-1.75 per mil to -0.75 per mil) in Tanner Basin during the last 200 k.y. is overprinted with smaller fluctuations correlated with climate change. The coolest intervals during the last glacial maximum (MISs 2 and 4) exhibit lower benthic d13C values, which correlate with global 13C shifts. The opposite relationship is exhibited during the last interglacial before 85 ka, when lower benthic d13C values are associated with warmer intervals (marine isotope Substages 5c and 5e) of the last interglacial. These time intervals were also marked by decreased intermediate water ventilation. Increased dissolution and organic accumulation during Substages 5b and 5d are anticorrelated with the benthic d13C record. These results suggest that a delicate balance in intermediate water d13C has existed between the relative influences of global 13C and regional ventilation changes at the 1165-m water depth of Site 1014.

Literature review of elasmobranch bycatch and retention rate

To address growing concern over the effects of fisheries non-target catch on elasmobranchs worldwide, the accurate reporting of elasmobranch catch is essential. This requires data on a combination of measures, including reported landings, retained and discarded non-target catch, and post-discard survival. Identification of the factors influencing discard vs. retention is needed to improve catch estimates and to determine wasteful fishing practices. To do this we compared retention rates of elasmobranch non-target catch in a broad subset of fisheries throughout the world by taxon, fishing country, and gear. A regression tree and random forest analysis indicated that taxon was the most important determinant of retention in this dataset, but all three factors together explained 59% of the variance. Estimates of total elasmobranch removals were calculated by dividing the FAO global elasmobranch landings by average retention rates and suggest that total elasmobranch removals may exceed FAO reported landings by as much as 400%. This analysis is the first effort to directly characterize global drivers of discards for elasmobranch non-target catch. Our results highlight the importance of accurate quantification of retention and discard rates to improve assessments of the potential impacts of fisheries on these species.