Richard J. Behl

Biotic response to late Quaternary rapid climate switches in Santa Barbara Basin: Ecological and evolutionary implications

Benthic foraminiferal assemblages from Santa Barbara Basin exhibit major faunal and ecological switches associated with late Quaternary millennial- to decadal-scale global climate oscillations. Repeated turnovers of entire faunas occurred rapidly (<40--400 yr) without extinction or speciation in conjunction with Dansgaard-Oeschger shifts in thermohaline circulation, ventilation, and climate, confirming evolutionary model predictions of Roy et al. Consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late Quaternary and possibly other transitional intervals in the history of the Earth`s ocean-atmosphere-cryosphere system. These data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change.

Influence of mechanical stratigraphy and kinematics on fault scaling relations

In order to document effects of mechanical anisotropy, fault geometry, and structural style on displacement-length (D-L) scaling relations, we investigated fault dimensions in the lithologically heterogeneous Monterey Formation exposed along Arroyo Burro Beach, California. The faults, which range in length from several centimeters to several meters, group into two populations: small faults confined to individual mudstone beds, and larger faults that displace multiple beds and often merge into bedding plane detachments. Whereas a linear correlation exists between displacement and length for small faults, displacement across large faults is independent of length. We attribute this deviation from scale-invariance to a combination of geologic factors that influence fault growth once faults extend beyond the confines of mudstone beds. Propagation of large faults across higher moduli opal-CT porcellanite leads to a reduction in DL, as does the development of drag folds. Further scatter in DL occurs when fault tips splay as they approach detachments. Large faults eventually merge into bedding plane detachments, which originally formed due to flexural slip folding. Extremely high DL ratios are recorded for these merged faults as they accommodate block rotation within a simple shear zone. Thus, both mechanical stratigraphy and the temporal evolution of fault systems can lead to a breakdown in fault scaling relations thought to characterize isolated fault growth in a homogeneous medium.

Climatically driven emissions of hydrocarbons from marine sediments during deglaciation

Marine hydrocarbon seepage emits oil and gas, including methane (≈30 Tg of CH4 per year), to the ocean and atmosphere. Sediments from the California margin contain preserved tar, primarily formed through hydrocarbon weathering at the sea surface. We present a record of variation in the abundance of tar in sediments for the past 32,000 years, providing evidence for increases in hydrocarbon emissions before and during Termination IA [16,000 years ago (16 ka) to 14 ka] and again over Termination IB (11–10 ka). Our study provides direct evidence for increased hydrocarbon seepage associated with deglacial warming through tar abundance in marine sediments, independent of previous geochemical proxies. Climate-sensitive gas hydrates may modulate thermogenic hydrocarbon seepage during deglaciation.

Vertical oxygen minimum zone oscillations since 20 ka in Santa Barbara Basin: A benthic foraminiferal community perspective

[1] Here we present a history of deoxygenation of upper intermediate waters during the last deglaciation from Santa Barbara Basin (SBB), based on quantitative analyses of benthic foraminiferal assemblages, from a new shallow piston core above basin sill depth (MV0811-15JC, 418m), and previously described sequences in the deeper basin (MD02-2504, 481m and MD02-2503, 570m). We document a 152m depth transect of benthic foraminiferal assemblages to extract changing community structure (density, diversity, and evenness) and improve paleoenvironmental interpretation of late Quaternary vertical oscillations in the upper boundary of the oxygen minimum zone (OMZ). Close interaction between changes in open margin OMZ and that of the restricted SBB is documented using these quantitative techniques. MV0811-15JC, while being unlaminated, contains strongly hypoxic foraminiferal assemblages (including species Bolivina tumida and Nonionella stella), coeval with preserved sediment laminations in the deeper cores. Last Glacial Maximum (LGM) assemblages across this transect contained oxic fauna and high diversity. At 14.7ka, glacial termination IA, hypoxic benthic fauna appeared across the transect, recording hypoxic waters (<0.5mlL 1 ) <300m from the ocean surface. Bolling/Allerod (B/A) assemblages uniquely stand out in the record, exhibited by low density, diversity, and evenness, and taxonomic composition reflecting extreme and stressful hypoxia and methane-rich environments. Younger Dryas assemblages were diverse and composed of oxic fauna, similar to LGM assemblages. Termination IB initiated another deoxygenation shift, followed by OMZ-associated faunal and density patterns. This analysis strengthens the quantitative assessment of oxygen concentrations involved in deglacial OMZ change and reveals the unexpected, remarkable shallowness of OMZ influence during the B/A.

Santa Barbara basin study extends global climate record

A fundamental goal of Earth science is to understand the remarkable instability of late Quaternary global climate prior to the beginning of the Holocene, about 11,000 years ago. This unusual climate behavior was characterized by millennial-scale climate oscillations on suborbital timescales, and a distinctive ‘sawtooth’ pattern of very abrupt glacial and stadial terminations (within decades) followed by more gradual global cooling [e.g., Dansgaard et al., 1993; Hendy and Kennett, 1999]. The fact that both major (glacial) and minor (stadial) cooling periods in Earths climate were terminated by similar abrupt warming episodes suggests a common mechanism driving such rapid changes in global climate. Understanding the causes of this instability is crucial given developing concerns about global warming, yet knowledge about this climate behavior has been essentially confined to the last 150,000 years or so, owing to the absence of available sequences of sufficient age and chronological resolution. The high-resolution paleoclimate record from the Greenland ice cores is limited to about 110 thousand years ago (ka),and although Antarctic ice cores now extend back to more than 740 ka [European Project for Ice Coring in Antarctica, 2004], these latter cores primarily provide information about high-latitude conditions at much lower resolution than is required to address abrupt climate change.

Enhancing Diversity in the Geosciences.

Abstract An innovative interdisciplinary project at California State University, Long Beach, was designed to increase the attractiveness of the geosciences (physical geography, geology, and archaeology) to underrepresented groups. The goal was to raise awareness of the geosciences by providing summer research opportunities for underrepresented high school and community college students and their faculty. A survey of a larger sample provided insight into strategies for enhancing geoscience awareness. A qualitative evaluation pointed to its success in meeting project goals. This unprecedented level of collaboration has set the groundwork for an institutional shift for inclusion of minorities in the geosciences and warrants replication.

Ethnic differences in geoscience attitudes of college students

While a gender balance remains elusive in the geosciences [de Wet et al., 2002], the underrepresentation of ethnic minorities in these fields is at least as great a concern. A number of cultural and social factors have been proposed to explain the poor ethnic minority representation in the geosciences, including limited exposure to nature, deficient academic preparation, inadequate financial resources to pursue higher education, ignorance of career opportunities in the geosciences, insufficient family support, and misconceptions of the field.

Glacial demise and methane's rise

The historical sciences—geology, archeology, and cosmology—test hypotheses differently than the experimental, laboratory sciences. When the process or event being investigated took place long ago or at a great distance from the investigators, hypotheses are tested by assembling key data that can support or refute the likelihood of the proposed explanation. In this way, we have developed understanding and agreement on many major events in Earth history, such as the Cretaceous–Tertiary extinction or the glacial–interglacial cycles of the Pleistocene epoch. A consilience of findings is required, and in a mechanistic, causative model, timing is of critical importance. If a key factor in the explanation can be shown to have occurred at a time inconsistent with the model—too early or too late—the hypothesis has to be modified or rejected. In PNAS, Reyes and Cooke (1) apply a refined dating approach to assess the timing of deglacial environmental change across the high-latitude circumpolar Arctic and its relation to increases in a major atmospheric greenhouse gas, methane. In their study, these investigators use improved methods for presentation and interpretation of the initiation dates for a very large dataset of Arctic peatland, tundra, and thermokarst sites to demonstrate that their development occurred too late to be the principal cause of impressively abrupt and large methane increases in atmospheric methane abundance at the beginning of the Bolling and the end of the Younger Dryas climatic intervals of the last deglaciation (2).

Abrupt termination of Marine Isotope Stage 16 (Termination VII) at 631.5 ka in Santa Barbara Basin, California

The Marine Isotope Stage 16–15 boundary (Termination VII) is the first deglacial warming step of the late Quaternary following the mid-Pleistocene transition (MPT), when 41 kyr climatic cycles shifted to strong 100 kyr cycles. The detailed structure of this important climatic event has remained unknown until now. Core MV0508-19JPC from Santa Barbara Basin, California, contains a decadal-scale climatic and geochemical sediment record of 4000 years duration that includes the early part of this deglacial episode. This record reveals that the climatic shift during the early deglacial occurred rapidly (<700 years), in a progression of three abrupt warming steps. The onset of Marine Isotope Stage (MIS) 15 was remarkably abrupt with 4–5°C sea surface warming in ~50 years. The deglacial sequence contains the well-dated Lava Creek tephra (631.3 ± 4 ka) from Yellowstone Caldera used to date the onset of Termination VII at 631.5 ka. The late MIS 16 and early MIS 15 interval exhibits multiple decadal-scale negative excursions in δ13C of planktic foraminifera, likely the result of repeated discharges of methane from methane hydrates associated with both ocean warming and low sea level. A warm interstadial that interrupts late MIS 16 is marked by elevated concentrations of redox-sensitive elements indicating sulfidic, oxygen-deficient bottom and pore-waters, and elevated concentrations of total organic carbon and Cd, reflecting increased surface productivity. Unlike younger sediments on the California margin, these indicators of increased productivity and low dissolved oxygen do not consistently correspond with each other or with preserved laminations, possibly reflecting instability of a still evolving ocean-atmosphere system following the MPT.