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

Sami Jokinen, Joonas J. Virtasalo, Tom Jilbert, Jerome Kaiser, Olaf Dellwig, Helge W. Arz, Jari Hänninen, Laura Arppe, Miia Collander, Timo Saarinen

Research output: Contribution to journalArticleScientificpeer-review

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.
Original languageEnglish
JournalBiogeosciences
Volume15
Issue number13
Pages (from-to)3975-4001
Number of pages27
ISSN1726-4170
DOIs
Publication statusPublished - 5 Jul 2018
MoE publication typeA1 Journal article-refereed

Fields of Science

  • SEDIMENTARY ORGANIC-MATTER
  • ATMOSPHERIC LEAD POLLUTION
  • ARCHIPELAGO SEA
  • MARINE-SEDIMENTS
  • LATE HOLOCENE
  • STOCKHOLM ARCHIPELAGO
  • SOURCE IDENTIFICATION
  • CYANOBACTERIA BLOOMS
  • EPICONTINENTAL BASIN
  • ESTUARINE SEDIMENTS
  • 1172 Environmental sciences

Cite this

Jokinen, Sami ; Virtasalo, Joonas J. ; Jilbert, Tom ; Kaiser, Jerome ; Dellwig, Olaf ; Arz, Helge W. ; Hänninen, Jari ; Arppe, Laura ; Collander, Miia ; Saarinen, Timo. / A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century. In: Biogeosciences. 2018 ; Vol. 15, No. 13. pp. 3975-4001.
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title = "A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century",
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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author = "Sami Jokinen and Virtasalo, {Joonas J.} and Tom Jilbert and Jerome Kaiser and Olaf Dellwig and Arz, {Helge W.} and Jari H{\"a}nninen and Laura Arppe and Miia Collander and Timo Saarinen",
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Jokinen, S, Virtasalo, JJ, Jilbert, T, Kaiser, J, Dellwig, O, Arz, HW, Hänninen, J, Arppe, L, Collander, M & Saarinen, T 2018, 'A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century' Biogeosciences, vol. 15, no. 13, pp. 3975-4001. https://doi.org/10.5194/bg-2018-25

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century. / Jokinen, Sami; Virtasalo, Joonas J.; Jilbert, Tom; Kaiser, Jerome; Dellwig, Olaf; Arz, Helge W.; Hänninen, Jari; Arppe, Laura; Collander, Miia; Saarinen, Timo.

In: Biogeosciences, Vol. 15, No. 13, 05.07.2018, p. 3975-4001.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

AU - Jokinen, Sami

AU - Virtasalo, Joonas J.

AU - Jilbert, Tom

AU - Kaiser, Jerome

AU - Dellwig, Olaf

AU - Arz, Helge W.

AU - Hänninen, Jari

AU - Arppe, Laura

AU - Collander, Miia

AU - Saarinen, Timo

PY - 2018/7/5

Y1 - 2018/7/5

N2 - 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.

AB - 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.

KW - SEDIMENTARY ORGANIC-MATTER

KW - ATMOSPHERIC LEAD POLLUTION

KW - ARCHIPELAGO SEA

KW - MARINE-SEDIMENTS

KW - LATE HOLOCENE

KW - STOCKHOLM ARCHIPELAGO

KW - SOURCE IDENTIFICATION

KW - CYANOBACTERIA BLOOMS

KW - EPICONTINENTAL BASIN

KW - ESTUARINE SEDIMENTS

KW - 1172 Environmental sciences

U2 - 10.5194/bg-2018-25

DO - 10.5194/bg-2018-25

M3 - Article

VL - 15

SP - 3975

EP - 4001

JO - Biogeosciences

JF - Biogeosciences

SN - 1726-4170

IS - 13

ER -