Hypoxia in the Eemian: mollusc faunas and sediment mineralogy from Cyprina Clay in the southern Baltic region

Abstract

The Cyprina Clay at Mommark, southern Denmark, contains a unique record of a shallow threshold‐controlled fjord environment through an entire interglacial. Today, the area suffers from periodic severe hypoxia, and the Eemian mollusc faunas (dominated by the hypoxia‐tolerant Corbula gibba and Arctica islandica), the sediments' varying content of pyrite, calcite and gypsum, as well as evidence of shell‐dissolution all show that the area also suffered from oxygen stress during the Eemian. A comparison with previous faunal studies on Cyprina Clay indicates that the entire southwestern Baltic region suffered from oxygen stress of varying degree throughout the Eemian. At Mommark, the severity of hypoxia varies inversely with water depth, indicating control by sea level and water depth over the basin threshold. After an early phase of eustatic sea level rise came a prolonged period of isostatic emergence and regression. Although this isostasy pattern is different from the Holocene, the present isostatic uplift of the Baltic entranceways may have the same effect and add to the anthropogene hypoxia threat in the Baltic region.

Pollen stratigraphy of the Late Pleistocene sediments at Mommark, Als, South Denmark

“…Kristensen & Knudsen 2006;Funder & Balic-Zunic 2006). Following the independent astronomical chronology proposed by Shackleton et al (2003), which gives an age of 126 kyr for the beginning of the Eemian, the marine regression in the southwestern part of the Baltic Sea began at Â/115.40 kyr (cf.…”

Early Last Interglacial palaeoenvironments in the western Baltic Sea: benthic foraminiferal stable isotopes and diatom-based sea-surface salinity

“…The environmental development is, furthermore, discussed in relation to previously published results from the western Baltic, including studies of foraminifera and ostracods (Kristensen et al 2000), dinoflagellate cyst assemblages (Head 2007) and molluscs (Nielsen et al 2007) from the Ristinge Klint section, as well as environmental proxies for the almost complete Eemian marine sequence at Mommark (Eirı´ksson et al 2006;Funder & Balic-Zunic 2006;Gibbard & Glaister 2006;Haila et al 2006;). Because of their location close to the Danish Belts ( Fig.…”

Eemian and Weichselian environmental development in the western Baltic area, NW Europe - Introduction

“…Molluscan assemblages show that the Eemian Baltic, like the present, generally suffered from oxygen stress (Funder & Balic-Zunic 2006). This is particularly pronounced in the Cyprina Clay around the western part of the Baltic, for instance at Mommark.…”

“…Forchammer 1842; Madsen et al 1908), occurred at c. 300 years after the beginning of the interglacial, while the marine regression happened at c. 10 600 (9/1000) years, within the upper part of regional pollen zone E7. This is indicated by the foraminiferal and ostracodal faunas , the molluscs (Funder & Balic-Zunic 2006), the diatoms (Haila et al 2006) and by the dinoflagellate cysts (Head unpublished). The record continues as freshwater, presumably lacustrine, deposits into the earliest Weichselian, as documented by ostracods .…”