Climate simulations suggest a collapse of the ocean circulation in the near future, resulting in conditions similar to past climates as reported by Intergovernmental Panel on Climate Change (IPCC) based on ample geological evidence. The THC incorporates density-driven vertical mixing process controlled by two major variables: temperature and salinity. While temperature is more influential in the surface ocean, salinity controls the deep ocean. Higher salinities enhance the THC, whereas lower salinities cause a slowdown or collapse of the THC, as is expected by the end of the 21st century due to ice melting. Despite the importance of deep ocean salinity in glacial-interglacial variations as models suggest, we lack a direct salinity proxy to reveal its role in past climates to understand future conditions. Here we ask: if we do not know the past ocean salinities and THC dynamics, how can we confidently rely on THC-related climate analogs for future conditions? To evaluate processes that impacted the THC with lower or higher salinities in the past, we urgently need to develop an independent and direct proxy for salinity, which is the objective of this project. Therefore, the sole objective of HowMOW is to explore a new direct and independent salinity proxy. To explore this new proxy, trace element analysis on fossil foraminifers, unicellular calcareous marine organisms, is applied by using advanced geochemical methods. Sodium/calcium values of fossil foraminifer shells are expected to reflect seawater salinities.
The ultimate goal of this project is to explore the role of salinity variation in the deep thermohaline circulation during the major climate shifts in the geological record. Towards achieving this goal, an important location is chosen: the Gulf of Cadiz. The Gulf of Cadiz is the location where the saltiest water mass, Mediterranean Outflow Water, exits the Mediterranean Sea and joins the Atlantic Ocean, and thus it is hypothesised that it played a significant role in THC variation during important climate shifts by being a salt injector to the THC. To test the efficacy of this new proxy, an important climate shift with ample data to compare in the study area is chosen: the Early-Middle Pleistocene Transition (EMPT). The EMPT resulted in the replacement of symmetric 41-kyr interglacial-glacial cycles with 100-kyr abrupt and asymmetric cycles about 1.2-07 million years ago. If deep-sea benthic foraminiferal Na/Ca is a proxy in paleoclimate studies, it should reflect a similar variation as obtained from continuous sediment cores recovered from the Gulf of Cadiz.
HowMOW relates to Sustainable Development Goals 13 and 14 of United Nations, which are Climate Action and Life Below Water, respectively. Climate Action aims at reducing the impact of global warming. Accordingly, "tropicalization" of the Mediterranean Sea is an ongoing phenomenon, which is described as the increase in tropic and alien invasive species in the region linked to increased temperature and salinity of the seawaters linked to global warming. Increase of non-endemic biota is adversely affecting the marine ecosystem of the Mediterranean Sea, altering the marine food web and eventually fisheries industry. Furthermore, it is suggested that mass mortality of the endemic bivalve Pinna nobilis, which is an endangered species listed by the International Union for Conservation of Nature (IUCN), is caused by a pathogen which thrives in increased salinity and high temperatures, linked to global warming. The proxy aimed at within HowMOW directly answers to one of the governing parameters of the tropicalization phenomenon and the habitable ecosystem of endemic species. The outcomes of HowMOW will potentially open doors into a more detailed research to reveal the onset of tropicalization, combined with other geochemical parameters contributing to scientific advancement, providing a new tool in paleoclimate research. Once proven for geological time scales, it can be applied for decadal time scales to research the impacts of global warming with associated parameters towards appropriate adaptation and mitigation acts providing essential information to policymakers.
