Details

Autor(en) / Beteiligte

• Ni, S.
• Quintana Krupinski, N. B.
• Groeneveld, J.
• Fanget, A. S.
• Böttcher, M. E.
• Liu, B.
• Lipka, M.
• Knudsen, K. L.
• Naeraa, T.
• Seidenkrantz, M.‐S.
• Filipsson, H. L.

Titel

Holocene Hydrographic Variations From the Baltic‐North Sea Transitional Area (IODP Site M0059)

Ist Teil von

• Paleoceanography and paleoclimatology, 2020-02, Vol.35 (2), p.n/a

Ort / Verlag

Hoboken: Blackwell Publishing Ltd

Erscheinungsjahr

2020

Link zum Volltext

Quelle

Wiley-Blackwell Journals

Beschreibungen/Notizen

• Deoxygenation affects many continental shelf seas across the world today and results in increasing areas of hypoxia (dissolved oxygen concentration ([O2]) <1.4 ml/L). The Baltic Sea is increasingly affected by deoxygenation. Deoxygenation correlates with other environmental variables such as changing water temperature and salinity and is directly linked to ongoing global climate change. To place the ongoing environmental changes into a larger context and to further understand the complex Baltic Sea history and its impact on North Atlantic climate, we investigated a high accumulation‐rate brackish‐marine sediment core from the Little Belt (Site M0059), Danish Straits, NW Europe, retrieved during the Integrated Ocean Drilling Program (IODP) Expedition 347. We combined benthic foraminiferal geochemistry, faunal assemblages, and pore water stable isotopes to reconstruct seawater conditions (e.g., oxygenation, temperature, and salinity) over the past 7.7 thousand years (ka). Bottom water salinity in the Little Belt reconstructed from modeled pore water oxygen isotope data increased between 7.7 and 7.5 ka BP as a consequence of the transition from freshwater to brackish‐marine conditions. Salinity decreased gradually (from 30 to 24) from 4.1 to ~2.5 ka BP. By using the trace elemental composition (Mg/Ca, Mn/Ca, and Ba/Ca) and stable carbon and oxygen isotopes of foraminiferal species Elphidium selseyensis and E. clavatum, we identified that generally warming and hypoxia occurred between about 7.5 and 3.3 ka BP, approximately coinciding in time with the Holocene Thermal Maximum (HTM). These changes of bottom water conditions were coupled to the North Atlantic Oscillation (NAO) and relative sea level change. Plain Language Summary The Baltic Sea is an intracontinental sea connected to the North Atlantic Ocean with large economic and societal values. It is sensitive to salinity and temperature changes and low oxygen conditions in the bottom water. The Little Belt is a transitional area between the central Baltic Sea and the North Sea. It is an ideal area to study the changes of freshwater outflow and saline water inflow and how the dynamics vary in relation to larger‐scale climate changes. We have reconstructed past seawater conditions (e.g., temperature, salinity and oxygenation) in the Baltic by geochemically analyzing microfossil (foraminifera) shells. We analyzed the trace elemental concentration and stable oxygen and carbon isotopes in calcite shells of low‐oxygen tolerant foraminiferal species as well as the benthic foraminiferal assemblages from a sediment core originating from the Little Belt covering the past 7,700 years. The salinity increased dramatically ~7,700–7,500 years ago and decreased ~4,100–2,500 years ago. Variation in bottom water oxygen content and bottom water temperature coincide. Our study highlights the benefit of using modern marine monitoring data together with a multiproxy approach to establish the link between local hydrographic conditions and regional climate changes and to explain how the environment has developed over time. Key Points Foraminiferal geochemistry, faunal, and pore water δ18O data document changes in temperature, salinity, and oxygen concentration over the last 7.7 kyr The bottom water in the Little Belt was warmer and hypoxic ~7.5‐3.3 ka BP and became fresher, cooler and more ventilated since ~4.1 ka BP Reconstructed bottom water conditions are linked to large scale climate variability related to the NAO and relative sea level change