Figure 1. Genetically identical G. ruber (sensu stricto) chromotypes A) pink and B) white.

Figure 1. Genetically identical G. ruber (sensu stricto) chromotypes A) pink and B) white.

Poster presented at the Fall meeting of the Geological Society of America, Summer of 2015

(Sarah McGrath, NSF REU Summer Intern Project)

Globigerinoides ruber (d’Orbigny, 1839) is one of the most commonly used planktonic foraminifera in paleoceanographic reconstructions. The calcium carbonate shells of these unicellular organisms are abundant in the marine fossil record and have proven invaluable in reconstructing past sea surface temperature and salinity, and in providing radiocarbon dates for stratigraphic control and information about ocean stratification. The majority of published research has focused on the widely-distributed white variant of G. ruber, but a pink form is also abundant in the Atlantic Ocean (and historically in the Pacific and Indian Oceans) (Fig. 1). The reason for and function of the difference in pigmentation is not well understood (Aurhas et al., 1981), and although offsets in the shell geochemistry of these two chromotypes has been demonstrated regionally in the Gulf of Mexico (Richey et al., 2012), they remain largely unexplored and unexplained. 

Figure 2. Core tops from cruise JC094 used in the G. ruber chromotype study. Five coretops were analyzed, one cluster from the western Atlantic and another in the eastern Atlantic.

Figure 2. Core tops from cruise JC094 used in the G. ruber chromotype study. Five coretops were analyzed, one cluster from the western Atlantic and another in the eastern Atlantic.

Previous research has suggested that the abundance of the two chromotypes varies seasonally (Richey et al., 2012) and so we proposed to investigate and utilize this ecological difference to reconstruct seasonal differences in temperature, salinity and watermass stratification in coretops spanning the Atlantic (Fig. 2) and generate a downcore record extending over the last glacial cycle. Exploring this additional measurement on an existing proxy has the potential to add valuable information to our paleoclimate knowledge base; furthermore this project created the opportunity for a graduate student to mentor and supervise an undergraduate summer intern interested in pursuing paleoceanographic research.

Funding generously provided by NSF and the Columbia University Climate Center