GSA Connects 2022 meeting in Denver, Colorado

Paper No. 169-32
Presentation Time: 9:00 AM-1:00 PM


YAGER, Stacy, Dept. of Environment, Geology, and Natural Resources, Ball State University, Muncie, IN 47306 and FLUEGEMAN, Richard, Environment, Geology, and Natural Resources Department, Ball State University, Fine Arts Building (AR), Room 117, Muncie, IN 47306-4554

Ocean freshening, along with ocean acidification, has become a recent threat to the ocean ecosystems. With increasing loss of sea ice and runoff, freshwater lenses will become more prevalent, resulting in biological and chemical shifts in the ocean stratification. The Cariaco Basin is a well-known semi-enclosed basin (maximum depth of 1400 m) and is the second-largest anoxic marine body in the world. This basin is located on the northern continental shelf of Venezuela and is considered a structural, pull-apart depression basin with restricting bottom water circulation into the open ocean. Late Quaternary (Marine Isotope Stages 1-9) sediment from Ocean Drilling Program (ODP) Leg 165 Site 1002c, located on the saddle between two smaller sub-basins, consists of one formal lithologic unit and eight sub-units. The formal unit consists of primarily olive gray to greenish gray nannofossil silty clays with intervals of abundant clays, diatoms, and foraminifers. Site 1002c was selected because of (1) the presence of laminated sediments noted in the core, (2) high sedimentation rates (~350 m/m.y), and (3) its location in a climatically sensitive region of the Caribbean Sea.

Extensive stable isotope work has been done at Site 1002c with oxygen isotopes (δ18O), using both benthic and planktonic foraminifers. Studies of carbon isotopes (δ13C) obtained from planktonic foraminifers remain incomplete. The mixed layer dwelling planktonic foraminifer, Orbulina universa, has been selected for the stable isotope measurements in this study.

Fresh water runoff from continental sources is enriched in 16O. Previous studies of δ18O at ODP site 1002 indicate a strong local influence on the isotopic record when compared to global ice volume records of δ18O from outside the Cariaco Basin. By utilizing the δ13C record of Orbulina universa, an understanding of local productivity in response to cycles of localized increased ocean freshening within the basin from river runoff can be made. It is expected that the cycles of freshwater fluctuations will be detected in the δ13C and δ18O records at ODP site 1002c. This will provide an understanding of the interactions between local biotic productivity and ocean basin freshening of wet and dry periods in the Cariaco Basin and be used as a modern analogue for future deep time studies.