Toward a standard stratigraphical classification practice for the <scp>B</scp>altic <scp>S</scp>ea sediments: the <scp>CUAL</scp> approach

Virtasalo, Joonas J.; Hämäläinen, Jyrki; Kotilainen, Aarno

doi:10.1111/bor.12076

Cited by 28 publications

(36 citation statements)

References 78 publications

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“…The sediment fill of the Archipelago Sea since the deglacial to present comprises a succession of ice-proximal tills and outwash, glaciolacustrine rhythmites, patchily distributed debrites, postglacial lacustrine clays, and brackishwater mud drifts (Virtasalo et al, 2007(Virtasalo et al, , 2014. The study area was deglaciated at ∼ 11 400 cal BP (Stroeven et al, 2016), which led to freshwater conditions in the area (Tuovinen et al, 2008).…”

Section: Study Locationmentioning

confidence: 99%

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

et al. 2018

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Abstract. The anthropogenically forced expansion of coastal hypoxia is a major environmental problem affecting coastal ecosystems and biogeochemical cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea whose central deep basins have been highly prone to deoxygenation during its Holocene history, as shown previously by numerous paleoenvironmental studies. However, long-term data on past fluctuations in the intensity of hypoxia in the coastal zone of the Baltic Sea are largely lacking, despite the significant role of these areas in retaining nutrients derived from the catchment. Here we present a 1500-year multiproxy record of near-bottom water redox changes from the coastal zone of the northern Baltic Sea, encompassing the climatic phases of the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA), and the Modern Warm Period (MoWP). Our reconstruction shows that although multicentennial climate variability has modulated the depositional conditions and delivery of organic matter (OM) to the basin the modern aggravation of coastal hypoxia is unprecedented and, in addition to gradual changes in the basin configuration, it must have been forced by excess human-induced nutrient loading. Alongside the anthropogenic nutrient input, the progressive deoxygenation since the beginning of the 1900s was fueled by the combined effects of gradual shoaling of the basin and warming climate, which amplified sediment focusing and increased the vulnerability to hypoxia. Importantly, the eutrophication of coastal waters in our study area began decades earlier than previously thought, leading to a marked aggravation of hypoxia in the 1950s. We find no evidence of similar anthropogenic forcing during the MCA. These results have implications for the assessment of reference conditions for coastal water quality. Furthermore, this study highlights the need for combined use of sedimentological, ichnological, and geochemical proxies in order to robustly reconstruct subtle redox shifts especially in dynamic, non-euxinic coastal settings with strong seasonal contrasts in the bottom water quality.

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Section: Study Locationmentioning

confidence: 99%

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

et al. 2018

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“…Virtasalo et al . () proposed the incorporation of the allostratigraphical and lithostratigraphical approach when interpreting data from the Baltic Sea region owing to its relevance for regional setting. Therefore, in this paper, it was decided to establish a sequence‐stratigraphical classification for the interpreted seismic data set together with sediment cores and 14 C ages and afterwards relate the classification to the so‐called Baltic Sea stages.…”

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confidence: 99%

The Holocene Great Belt connection to the southern Kattegat, Scandinavia: Ancylus Lake drainage and Early Littorina Sea transgression

Bendixen

Jensen

Boldreel

et al. 2015

Boreas

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Late-and postglacial geological evolution of the southern Kattegat connection to the Great Belt was investigated from high-resolution seismic data and radiocarbon-dated sediment cores in order to elucidate the Ancylus Lake drainage/Littorina Sea transgression. It was found that glacial deposits form the acoustic basement and are covered by Lateglacial (LG) marine sediments and postglacial (PG; Holocene) material. The LG deposits form a highstand systems tract, whereas the PG deposits cover a full depositional sequence, consisting of a lowstand systems tract (PG I), transgressive systems tract (PG II; subdivided into three parasequences) and finally a highstand systems tract (PG III). PG I sand deposits (11.7-10.8 cal. ka BP) are found in a major western channel and in a secondary eastern channel. PG II (10.8-9.8 cal. ka BP) consists of estuarine and coastal deposits linked to an estuary located at the mouth of the channels. Both channels drained fresh water from south to north. The PG III, that is younger than 9.8 cal. ka BP, represents the threshold marine flooding at the southeastern branch of the palaeo-Great Belt channel. At 9.3 cal. ka BP, fully marine conditions were established, shortly before the flooding of the threshold to the northern part of the Great Belt. These early Holocene spits and sand bars are preserved as features on the present seabed, probably as a result of the rapid sea-level rise that led to back-stepping of the early Holocene palaeo-coast system. This study shows no evidence of major erosion or delta deposition linked to the emptying of the Ancylus Lake, which suggests that continuous water flow from the south characterized the area, without any major drainage event of the Ancylus Lake impacting the southwestern Kattegat.

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“…Sub-bottom profiler and side-scan sonar data were collected and interpreted using Meridata MDCS and MDPS software. The seismic units and corresponding sediment types were interpreted following Virtasalo et al (2007Virtasalo et al ( , 2014. Sound velocities used for converting the seismic two-way travel time to sediment unit thickness were as follows: brackishwater mud, 1480 m s −1 ; postglacial lacustrine and glaciolacustrine clay, 1550 m s −1 ; subaqueous ice-contact fan deposits, 1600 m s −1 ; and till, 1850 m s −1 (Sviridov, 1977;Virtasalo et al, 2014).…”

Section: Methodsmentioning

confidence: 99%

“…The First Salpausselkä was deposited as a narrow ridge of contiguous meltwater fans and local feeding eskers that were formed along the ice-margin grounding line (Virkkala, 1963;Glückert, 1986;Fyfe, 1990;Kujansuu et al, 1993) in an icecontact lake that was more than 100 m deep in Hanko (Fyfe, 1990). After the ice-margin retreat, the till and subaqueous ice-contact fan deposits were successively covered by glaciolacustrine rhythmically alternating (varved) silt and clay, and postglacial lacustrine poorly bedded clay (Virtasalo et al, 2007(Virtasalo et al, , 2014. At ca.…”

Section: Study Areamentioning

confidence: 99%

“…At ca. 7600 years ago, the deposition of postglacial lacustrine clay came to an end with erosion and the emplacement of a thin transgressive silt-sand sheet as a result of the mid-Holocene marine flooding and establishment of brackish-water conditions in the Baltic Sea Basin (Virtasalo et al, 2007(Virtasalo et al, , 2016. The deposition soon resumed with the organic-rich brackish-water mud drift that is strongly influenced by waves and near-bottom currents, and still continues today.…”

Section: Study Areamentioning

confidence: 99%

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Submarine groundwater discharge site in the First Salpausselkä ice-marginal formation, south Finland

et al. 2019

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Abstract. Submarine groundwater discharge (SGD) has been implicated as a significant source of nutrients and potentially harmful substances to the coastal sea. Although the number of reported SGD sites has increased recently, their stratigraphical architecture and aquifer geometry are rarely investigated in detail. This study analyses a multifaceted dataset of offshore seismic sub-bottom profiles, multibeam and side-scan sonar images of the seafloor, radon measurements of seawater and groundwater, and onshore ground-penetrating radar and refraction seismic profiles in order to establish the detailed stratigraphical architecture of a high-latitude SGD site, which is connected to the Late-Pleistocene First Salpausselkä ice-marginal formation on the Hanko Peninsula in Finland. The studied location is characterized by a sandy beach, a sandy shore platform that extends 100–250 m seaward sloping gently to ca. 4 m water depth, and a steep slope to ca. 17 m water depth within ca. 50 m distance. The onshore radar and offshore seismic profiles are correlated based on unconformities, following the allostratigraphical approach. The aquifer is hosted in the distal sand-dominated part of a subaqueous ice-contact fan. It is interpreted that coarse sand interbeds and lenses in the distal fan deposits, and, potentially, sandy couplet layers in the overlying glaciolacustrine rhythmite, provide conduits for localized groundwater flow. The SGD takes place predominantly through pockmarks on the seafloor, which are documented on the shore platform slope by multibeam and side-scan sonar images. Elevated radon-222 activity concentrations measured 1 m above seafloor confirm SGD from two pockmarks in fine sand sediments, whereas there was no discharge from a third pockmark that was covered with a thin organic-rich mud layer. The thorough understanding of the local stratigraphy and the geometry and composition of the aquifer that have been acquired in this study are crucial for successful hydrogeological modelling and flux studies at the SGD site.

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Toward a standard stratigraphical classification practice for the Baltic Sea sediments: the CUAL approach

Cited by 28 publications

References 78 publications

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

The Holocene Great Belt connection to the southern Kattegat, Scandinavia: Ancylus Lake drainage and Early Littorina Sea transgression

Submarine groundwater discharge site in the First Salpausselkä ice-marginal formation, south Finland

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