Pteropods are excellent recorders of surface temperature and carbonate ion concentration

N Keul,R R Schneider,K T C A Peijnenburg,N Andersen,V Kitidis,E Goetze

doi:10.1038/s41598-017-11708-w

N Keul, R R Schneider + Show 4 more

Open Access

https://doi.org/10.1038/s41598-017-11708-w

Copy DOI

Abstract

Pteropods are among the first responders to ocean acidification and warming, but have not yet been widely explored as carriers of marine paleoenvironmental signals. In order to characterize the stable isotopic composition of aragonitic pteropod shells and their variation in response to climate change parameters, such as seawater temperature, pteropod shells (Heliconoides inflatus) were collected along a latitudinal transect in the Atlantic Ocean (31° N to 38° S). Comparison of shell oxygen isotopic composition to depth changes in the calculated aragonite equilibrium oxygen isotope values implies shallow calcification depths for H. inflatus (75 m). This species is therefore a good potential proxy carrier for past variations in surface ocean properties. Furthermore, we identified pteropod shells to be excellent recorders of climate change, as carbonate ion concentration and temperature in the upper water column have dominant influences on pteropod shell carbon and oxygen isotopic composition. These results, in combination with a broad distribution and high abundance, make the pteropod species studied here, H. inflatus, a promising new proxy carrier in paleoceanography.

Highlights

Assessing the future impact of ocean acidification, the decline in oceanic pH due to anthropogenic CO2 emissions, on marine ecosystems is difficult, as the complexity of ecosystems cannot be replicated in laboratory experiments
Deriving past ocean temperature and chemistry from fossil pteropod shells provides a wealth of information about past climate change events
The present study shows that the species H. inflatus is well suited for paleo-reconstructions, as the stable isotopic composition of their shells can be used to track two climate change indicators: δ18Optero records temperature (Fig. 3) and carbonate ion concentration is traced by δ13Cptero (Fig. 4a)

Summary

Introduction

Assessing the future impact of ocean acidification, the decline in oceanic pH due to anthropogenic CO2 emissions, on marine ecosystems is difficult, as the complexity of ecosystems cannot be replicated in laboratory experiments. One prominent and straightforward candidate for such an approximation (proxy) of past conditions is the oxygen isotopic composition (δ18O), which reflects ocean temperature[1] It has been demonstrated in inorganic precipitation studies as well as in direct measurements of biogenically produced calcium carbonate[2,3], that the calcium carbonatewater oxygen isotopic equilibrium is determined by temperature and (sea)water δ18O (δ18OSW; see Table 1 for notations). The approximately one year life cycle and diel vertical migrations of pteropods may yield a more integrative proxy record across epipelagic and mesopelagic water masses and across seasons in comparison to foraminifera, which are characterized by a shorter life span and potentially shallower calcification depths. The calibrations established here will be of use to the ocean acidification and paleo-oceanographic community, as the studied species, H. inflatus, occurs in high abundance in sediments worldwide[20], for instance, in the Central and South Atlantic[21] or the Caribbean Sea[22]

Methods

Results

Conclusion