Le Friant, A., Ishizuka, O., Stroncik, N.A., and the Expedition 340 Scientists Proceedings of the Integrated Ocean Drilling Program, Volume 340 Data report: the Late Quaternary fossil record of holoplanktonic gastropods at IODP Sites U1395 and U13941 Deborah Wall-Palmer,2 Christopher W. Smart,2 and Malcolm B. Hart2 Chapter contents Abstract Abstract . 1 Living holoplanktonic gastropods (pteropods and heteropods) are Introduction . 1 a common component of the zooplankton at all latitudes and are Methods . 2 highly sensitive indicators of surface ocean changes. Despite hav- ing a fossil record that may extend from the Jurassic, there are few Results . 3 detailed stratigraphic sequences of holoplanktonic gastropods Conclusions . 4 and, consequently, they are rarely used in biostratigraphy. This is Acknowledgments. 4 largely due to the susceptibility of their delicate aragonitic shells References . 5 to dissolution. However, in well-preserved sediments, fossil hol- Figures . 7 oplanktonic gastropods have the potential to contribute valuable Tables. 15 information for paleoceanography, paleoecology, and strati- graphic correlation. Here we present a ~300 ky record of holoplanktonic gastropods from two sites cored/drilled offshore of Montserrat during Inte- grated Ocean Drilling Program (IODP) Expedition 340. Oxygen isotope stratigraphy was used to produce a stratigraphic frame- work for each site, which was compared and correlated to the cor- responding downcore abundances of holoplanktonic gastropods. In addition, the record of previously cored Site CAR-MON 2, ~15 km southwest of IODP Site U1396, was compared to data at Sites U1395 and U1394 to identify species associations that are repro- ducible across the area. A number of downhole distributions were found to correlate significantly across the three sites, highlighting ten key species, three of which (Heliconoides inflatus, Creseis clava, and Atlanta plana) display significant relationships to multiple holoplanktonic gastropod species. Fluctuations in species abun- dance were found not to be related to changes in temperature, lo- cally or globally, and were more likely to indicate predator-prey relationships or competition for prey. This made holoplanktonic gastropod assemblages unsuitable as stratigraphic markers in this area but improves our understanding of holoplanktonic gastro- 1Wall-Palmer, D., Smart, C.W., and Hart, M.B., 2015. Data report: the Late Quaternary fossil pod ecology in the Caribbean Sea. record of holoplanktonic gastropods at IODP Sites U1395 and U1394. In Le Friant, A., Ishizuka, O., Stroncik, N.A., and the Expedition 340 Scientists, Introduction Proceedings of the Integrated Ocean Drilling Program, 340: Tokyo (Integrated Ocean Drilling Holoplanktonic gastropods are uniquely adapted to live their en- Program Management International, Inc.). tire lives within the plankton. They can reach densities of up to doi:10.2204/iodp.proc.340.203.2015 3 2School of Geography, Earth and Environmental 10,000/m , constituting an important component of the ocean Sciences, Plymouth University, Plymouth, PL4 8AA, food web at all latitudes (Fabry et al., 2008). There are two groups UK. Correspondence author: of holoplanktonic gastropods: pteropods (Thecosomata and Gym- [email protected] nosomata) and heteropods (Pterotracheoidea). Within these Proc. IODP | Volume 340 doi:10.2204/iodp.proc.340.203.2015 D. Wall-Palmer et al. Data report: the Late Quaternary fossil record groups there are shelled, partially shelled, and shell- Methods less species, although shell-less species still have a shell at the larval stage. Both pteropod and hetero- IODP Expedition 340 successfully collected cores pod shells are small, delicate, and formed of arago- from three sites (U1396, U1395, and U1394) offshore nite and are, consequently, particularly susceptible of Montserrat in the Lesser Antilles, Caribbean Sea to dissolution (Fabry, 1990) and mechanical damage. (Fig. F1). Sites U1395 and U1394 lie within the Their shells are, however, frequently preserved in Bouillante–Montserrat Graben, ~15 and ~33 km shallow warm-water regions that are supersaturated from the island, respectively, and in the path of ma- with respect to aragonite. Offshore of Montserrat, in jor submarine landslides (Trofimovs et al., 2013). an area of exceptional calcium carbonate preserva- Sedimentation at these two sites has been consider- tion, the fossil record of holoplanktonic gastropod ably affected by the input of volcanic material and shells within the sediments is rich and accurately re- resedimentation by density current deposits (Expedi- flects the living population at the time of deposition tion 340 Scientists, 2013). Here, we present a ~300 ky (Wall-Palmer et al., 2014b). Moreover, any sediment holoplanktonic gastropod record from Sites U1395 transport, such as density current deposits that are and U1394 that corresponds to ~166 and ~44 m hole depth, respectively. Material analyzed was collected common in this area (Watt et al., 2012; Trofimovs et from undisturbed hemipelagic sediments only and al., 2013; Cassidy et al., 2014), fragments the delicate the data are presented with gaps where disturbed shells, meaning that, where shells are present, their material interrupts the record. stratigraphy is unlikely to have been affected by re- working. All species of holoplanktonic gastropods The holoplanktonic gastropod content of Site U1396 presented here are extant, and living examples can is not presented here because the site does not pre- be found in the oceans today. serve a record of holoplanktonic gastropods between ~43 and 250 ky (Wall-Palmer et al., 2014a), despite Holoplanktonic gastropods are sensitive to environ- being positioned out of the main path of density cur- mental changes (Maas et al., 2012), so their fossil re- rent deposits. This absence was attributed to win- cord can be used as an archive of past ocean surface nowing by bottom water currents that are thought conditions (Wall-Palmer et al., 2013, 2014b). to have removed the delicate shells. Previously cored Changes in dominant holoplanktonic gastropod spe- Site CAR-MON 2 (Fig. F1) records a rich fossil record cies are often temperature driven, especially where of holoplanktonic gastropods (Le Friant et al., 2008; temperature has a large range over time (e.g., during Wall-Palmer et al., 2013, 2014b), despite being only the Late Pleistocene in the Mediterranean Sea [Sbaffi ~15 km southwest of Site U1396. Therefore, Site et al., 2001; Wall-Palmer et al., 2014b]). In the Lesser CAR-MON 2 was used as a comparison site, rather Antilles, however, where temperature variations are than Site U1396. All drilling and coring sites are smaller over time, changes in species abundance can above the aragonite lysocline, reducing any effects of be more difficult to interpret. Furthermore, there are postdepositional dissolution upon the aragonitic a number of holoplanktonic gastropods, in particu- gastropod shells. lar the heteropods, for which we know very little about their environmental preferences, despite being extant. This makes it difficult to use holoplanktonic Core sampling gastropods as stratigraphic marker species in such ar- Holes U1394A, U1394B, and U1395B were sampled eas and obstructs their potential as paleoceano- at ~50 cm intervals (10, 2, and 6 ky, respectively) graphic indicators. from 0 to 5.9, 91.8 to 166.1, and 0 to 43.6 meters be- In this study, we present the downcore distribution low seafloor (mbsf), respectively. All sampling was of all holoplanktonic gastropod shells found at Inte- carried out at the Gulf Coast Core Repository in Col- grated Ocean Drilling Program (IODP) Sites U1395 lege Station, Texas (USA). Samples were taken from and U1394. Although their analysis has not allowed hemipelagic sediment only to avoid the effects of re- detailed interpretations of the paleoceanography of working and volcanic input, which can dissolve hol- this area, a number of species associations have been oplanktonic gastropod shells (Wall-Palmer et al., identified. It is anticipated that these data will help 2011). Sample processing was carried out at Plym- to stimulate more widespread study of holoplank- outh University in the United Kingdom. Samples tonic gastropods in marine sediment cores, as well as were dried in an oven at 40°C for 24 h to facilitate contributing new ecological information that can be the subsequent removal of clay particles. Samples applied to living populations, in particular the het- were then rehydrated and washed over a 63 µm eropods, whose environmental requirements are cur- sieve. Both the <63 and >63 µm fractions were col- rently poorly known. lected, filtered, and dried in an oven at 40°C for 24 h. Proc. IODP | Volume 340 2 D. Wall-Palmer et al. Data report: the Late Quaternary fossil record Microfossil analysis CAR-MON 2 (Figs. F3, F4, F5). H. inflatus is a warm- water cosmopolitan species (Bé and Gilmer, 1977) For each sample, just more than 300 (or until the that tolerates a wide range of water temperatures sample was exhausted) holoplanktonic gastropod (14°C–28°C) (Table T1). This species is found in all specimens were counted and identified from the samples analyzed, indicating that the water offshore >150 µm size fraction. Only whole specimens were of Montserrat was 14°C–28°C at all times during the counted to avoid the distortion produced by several last 300 ky. fragments of the same specimen. Pteropod species identification was made using the keys published by Five further species (Atlanta