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Martina Hollstein

Dr. Martina Hollstein

Group:	Low Latitude Climate Variability
Phone:	+49 421 218-65533
Email:	[Bitte aktivieren Sie Javascript]
Room:	MARUM II, 3160

Research Interests

The overarching motivation for my research is to better understand past climate variability and underlying mechanisms. I am particularly interested in deciphering the role of oceans in climate change. Therefore, my research mainly focuses on ocean-climate linkages in key climatic regions. For my reconstructions, I apply a range of different proxies, mostly based on planktic foraminifera, and also collaborate with numerical modelers to gain a more comprehensive view on the palaeoceanographic interpretations of the proxy data. Other focus areas of research concern biogeochemical and oceanographic processes in the modern ocean, and the impact of anthropogenic activities on the deep-sea environment.

Projects

Rainfall variability in eastern Australia over the last 130 kyr (DFG, 2025-2027)

Eastern Australia is recurrently affected by severe droughts and floods that have tremendous effects on the ecological and socioeconomic systems of Australia. The regional rainfall variability is coupled to the Australasian monsoon and the El Niño-Southern Oscillation. Today, the sea surface temperature (SST) and vigor of the Pacific western boundary currents, particularly the East Australian Current (EAC), additionally influence rainfall along the east Australian coast with a warmer and stronger EAC promoting rainfall. However, the role of ocean temperatures in regulating the climate in eastern Australia is poorly understood. For instance, climate projections suggest that eastern Australia will experience long-term drying during the 21^st century despite a warmer EAC. Reconstructing past changes in rainfall over eastern Australia along with the SST and vigor of the western boundary currents is therefore critical to better understand their long-term connection.

The aim of this project is to reconstruct changes in east Australian rainfall and its relation to SST over the last glacial-interglacial cycle. To this end, records of planktic foraminiferal Mg/Ca (SST proxy) and records of compound-specific isotopes in plant leaf waxes (rainfall proxy) will be generated from marine sediment cores retrieved along a latitudinal transect at the East Australian margin. The reconstructions will also help to better assess the impact of future SST changes on Australian rainfall.

Monsoon dynamics

This project is part of the Cluster of Excellence “The Ocean Floor – Earth’s Uncharted Interface”, research unit “Ocean floor as recorder”. One of the main tasks of Recorder is the development of “warmer-than-present world” scenarios from ocean floor climate archives with the help of climate models. As part of this, it is intended to decipher changes in the global hydrological cycle in response to natural climate perturbations.

The Australasian monsoon systems constitute a central element of the global hydrological cycle. Facing its influence on the living conditions of billions of people, gaining a comprehensive understanding of monsoon dynamics, particularly under warm climate conditions, is an enduring issue with respect to global future warming. Paleoclimatic data show that monsoon rainfall is influenced by varying sea surface temperature (SST) (gradients), for instance in response to astronomical forcing. However, the connection between SST and monsoon rainfall has not been studied in a systematic approach yet. Besides, temperature simulation is one of the main sources of error for projecting future rainfall. Deciphering the coupling between SST and monsoonal rainfall is thus crucial to better understand monsoon dynamics and project the future development of monsoon systems.

In this project, we will use proxy-based reconstructions and model simulations to assess the coupling between SST and monsoon rainfall from the geological past. Particularly, we will compile available and newly generated SST and rainfall records from the Australasian monsoon realms to analyze existing trends and variability across the Holocene and previous interglacial periods as “warmer-than-present world” analogues. The proxy data basis will be combined with numerical model simulations that address the SST influence on monsoon rainfall.

Publications

Hollstein, M., Kienast, M., Lückge, A., Yokoyama, Y., Mohtadi, M. (2024). Sea surface temperatures across the Coral Sea over the last glacial-interglacial cycle. Paleoceanography and Paleoclimatology, 39, e2023PA004757. doi:10.1029/2023PA004757.
Haalboom, S., Schöning, T., Urban, P., Gazis, I.G., de Stigter, H., Gillard, B., Baeye, M., Hollstein, M., Purkiani, K., Reichert, G.-J., Thomsen, L., Haeckel, M., Vink, A., Greinert, J. (2022). Monitoring of anthropogenic sediment plumesin the Clarion-Clipperton Zone, NE equatorical Pacific Ocean. Frontiers in Marine Sciences, 9:882155. doi: 10.3389/fmars.2022.882155.
Purkiani, K., Gillard, B., Paul, A., Haeckel, M., Haalboom, S., Greinert, J., de Stigter, H., Hollstein, M., Baeye, M., Vink, A., Thomsen, L., Schulz, M. (2021). Numerical simulation of deep-sea sediment transport induced by a dredge experiment in the northeastern Pacific Ocean. Frontiers in Marine Sciences, 8:719463. doi:10.3389/fmars.2021.719463.
Hollstein, M., Mohtadi, M., Kienast, M., Rosenthal, Y., Oppo, D.W., Groeneveld, J., Southon, J.R., Lückge, A. (2020). The impact of astronomical forcing on surface and thermocline variability across the 1 Western Pacific Warm Pool over the past 160 kyr. Paleoceanography and Paleoclimatology, 35, e2019PA003832. doi:10.1029/2019PA003832.
Hollstein, M., Mohtadi, M., Rosenthal, Y., Prange, M., Oppo, D., Martínez Méndez, G., Tachikawa, K., Moffa Sanchez, P., Steinke, S., Hebbeln, D. (2018). Variations in Western Pacific Warm Pool surface and thermocline conditions over the past 110,000 years: Forcing mechanisms and implications for the glacial Walker circulation. Quaternary Science Reviews, 201, 429-445. doi:10.1016/j.quascirev.2018.10.030.
Hollstein, M., Mohtadi, M., Rosenthal, Y., Moffa Sanchez, P., Oppo, D., Martínez Méndez, G., Steinke, S., Hebbeln, D. (2017). Stable oxygen isotopes and Mg/Ca in planktic foraminifera from modern surface sediments of the Western Pacific Warm Pool: Implications for thermocline reconstructions. Paleoceanography, 32, doi:10.1002/2017PA003122.

Expeditions

SONNE-256 (TACTEAC) SW Pacific, Auckland (NZ) - Darwin (AUS), 17.04.-09.05.2017, Chief scientist: Mahyar Mohtadi