African American and Hispanic adolescent STI and pregnancy prevention: Whose responsibility is it, anyway?

This dissertation utilized quantitative and qualitative methods to examine the role of responsibility in the prevention of sexually transmitted infections (STIs) and pregnancy through condom use and other sexual behaviors among young adolescents. Data were analyzed across race and gender and three papers were developed. The quantitative portion used logistic regression to assess associations between personal responsibility, as well as other know correlates, and reported condom use and condom use intentions as a means of STI and pregnancy prevention among 445 inner-city, high school adolescents. Responsibility to prevent pregnancy by providing the condom was associated with condom use at last sex and consistent condom use. Responsibility to prevent acquiring a STI by using a condom was significantly associated with consistent condom use. No significant associations were found between responsibility and condom use intentions. ^ The qualitative section of the dissertation project involved conducting 28 in-depth interviews among 9th and 10th grade, African American and Hispanic students who attended a large urban school district in South Central Texas. Perceptions of responsibility for preventing STIs and unintended pregnancy, as well as for condom use, were explored. Male and female adolescents expressed joint responsibility to prevent a STI or pregnancy. Perceptions of responsibility for providing and using the condoms were mixed. Despite the indication of both partners, mostly all participants implied that females, more so than the males, had the final responsibility to prevent contracting a STI, a pregnancy, to provide a condom, and to make sure a condom was used. Participants expressed the role of parents' involvement for preventing these outcomes as well as the need for more sexual health education and access to preventative methods. ^ The last section of this dissertation involved qualitative inquiry to ascertain perceptions of reasons why adolescents engage in anal and oral (non-coital) sex. Pleasure-seeking and giving as well social influence and pressure were described as the main reasons why teenagers have non-coital sex. Other reasons included conveniences of participating in these behaviors such as ease of performing oral sex and anal sex as a convenient alternative to vaginal sex. Sexual inexperience was an indicator for why anal sex occurs. Many of the reasons involved misperceptions and adolescents who practice these sexual behaviors place themselves at-risk for contracting a STI. ^ This dissertation increased the current knowledge base about adolescent sexual responsibility and non-coital behaviors. Future studies should explore perceptions of responsibility and actual sexual activity practices among adolescents to reduce the burden of STIs and pregnancy as well as help public health professionals develop programs for adolescent populations, schools, and communities where these issues persist.^

Physical properties of sediments at DSDP Holes 78-541 and 78-543

Sediment cored within the Barbados subduction complex at Sites 541 and 542 are underconsolidated. Underconsolidation and changes in physical properties of the cored section can be related to excess pore water pressure that equals the lithostatic load at Site 542 and to major thrust faulting observed at Site 541. Apparently, the pore fluids within the subduction complex are absorbing the tectonic shock of underthrusting. Sediment sampled from the reference Site 543 on the adjacent Atlantic Plate are also underconsolidated. However, underconsolidation in Hole 543 is apparently due to the movement of excess nitrogen gas observed deeper in the hole. Excess gas was not observed at Sites 541 and 542.

Foraminiferal study of ODP Hole 189-1171

Sequence boundary ages determined in shallow-water sediments obtained from ODP (Ocean Drilling Program) Leg 189 Site 1171 (South Tasman Rise) compare well with other stratigraphic records (New Jersey, United States, and northwestern Europe) and d18O increases from deep-sea records, indicating that significant (>10 m) eustatic changes occurred during the early to middle Eocene (51-42 Ma). Sequence boundaries were identified and dated using lithology, bio- and magnetostratigraphy, water-depth changes, CaCO3 content, and physical properties (e.g., photospectrometry). They are characterized by a sharp bioturbated surface, low CaCO3 content, and an abrupt increase in glauconite above the surface. Foraminiferal biofacies and planktonic/benthic foraminiferal ratios were used to estimate water-depth changes. Ages of six sequence boundaries (50.9, 49.2, 48.5-47.8, 47.1, 44.5, and 42.6 Ma) from Site 1171 correlate well to the timings of d18O increases and sequence boundaries identified from other Eocene studies. The synchronous nature of sequence boundary development from globally distal sites and d18O increases indicates a global control and that glacioeustasy was operating in this supposedly ice-free world. This is supported by previous modeling studies and atmospheric pCO2 estimates showing that the first time pCO2 levels decreased below a threshold that would support the development of an Antarctic ice sheet occurred at ca. 51 Ma. Estimates of sea-level amplitudes range from ~20 m for the early Eocene (51-49 Ma) and ~25 m to ~45 m for the middle Eocene (48-42 Ma) using constraints established for Oligocene d18O records.

Global Ocean Particulate Organic Carbon flux merged with satellite parameters

The efficiency of the biological pump of carbon to the deep ocean depends largely on the biologically mediated export of carbon from the surface ocean and its remineralization with depth. Global satellite studies have primarily focused on chlorophyll concentration and net primary production (NPP) to understand the role of phytoplankton in these processes. Recent satellite retrievals of phytoplankton composition now allow for the size of phytoplankton cells to be considered. Here, we improve understanding of phytoplankton size structure impacts on particle export, remineralization and transfer. Particulate organic carbon (POC) flux observations from sediment traps and 234Th are compiled across the global ocean. Annual climatologies of NPP, percent microplankton, and POC flux at four time series locations and within biogeochemical provinces are constructed, and sinking velocities are calculated to align surface variables with POC flux at depth. Parameters that characterize POC flux vs. depth (export flux ratio, labile fraction, remineralization length scale) are then fit to the aligned dataset. Times of the year dominated by different size compositions are identified and fit separately in regions of the ocean where phytoplankton cell size showed enough dynamic range over the annual cycle. Considering all data together, our findings support the paradigm of high export flux but low transfer efficiency in more productive regions and vice versa for oligotrophic regions. However, when parsing by dominant size class, we find periods dominated by small cells to have both greater export flux and lower transfer efficiency than periods when large cells comprise a greater proportion of the phytoplankton community.

(Figure 2) Proxy records of sediment core GeoB6007-2

Central waters of the North Atlantic are fundamental for ventilation of the upper ocean and are also linked to the strength of the Atlantic Meridional Overturning Circulation (AMOC). Here, we show based on benthic foraminiferal Mg/Ca ratios, that during times of enhanced melting from the Laurentide Ice Sheet (LIS) between 9.0-8.5 thousand years before present (ka) the production of central waters weakened the upper AMOC resulting in a cooling over the Northern Hemisphere. Centered at 8.54 ± 0.2 ka and 8.24 ± 0.1 ka our dataset records two ~150-year cooling events in response to the drainage of Lake Agassiz/Ojibway, indicating early slow-down of the upper AMOC in response to the initial freshwater flux into the subpolar gyre (SPG) followed by a more severe weakening of both the upper and lower branches of the AMOC at 8.2 ka. These results highlight the sensitivity of regional North Atlantic climate change to the strength of central-water overturning and exemplify the impact of both gradual and abrupt freshwater fluxes on eastern SPG surface water convection. In light of the possible future increase in Greenland Ice Sheet melting due to global warming these findings may help us to better constrain and possibly predict future North Atlantic climate change.