An outline for Finnish Holocene tephrochronology: volcanic ash as a dating method in Finland

Tephrochronology is a high-precision dating method that uses volcanic ash horizons as isochrons in correlating and dating geological records and archaeological sites. First developed in the volcanic regions of the world, tephrochronology has expanded to ever more distal areas with improved laboratory and analytical methods that have enabled the utilization of even the scarcest deposits of far-travelled cryptotephra i.e. small volcanic glass shards that are invisible to the naked eye. The objective of this dissertation is to assess the potential of cryptotephra studies and tephrochronology in Finland. No cryptotephra studies had been conducted in Finland previously, and the ultimate aim of the work presented here was to establish a first outline for a Finnish tephrochronology that could be used as a dating tool in environmental research in the region. Cryptotephra was searched from 30 peatland and lake sites from an area that covers the whole southern and central Finland from Åland archipelago in the west to the Russian border in the east. As a result, cryptotephra deposits from at least 17 Icelandic and two Alaskan volcanic eruptions were detected and geochemically characterized from the Finnish environmental archives. The oldest identified tephra in Finland is the 7 ka Hekla 5 tephra and the youngest one is the Askja 1875 tephra. The Finnish tephrochronology therefore covers approximately 7000 years and the results of this study demonstrate that dispersal of tephra to Finland has been relatively frequent throughout this time. Within this project, the known dispersal areas of several Holocene tephras, such as Askja 1875, Hekla 1845, Hekla 1510, Landnám (Torfajökull), White River Ash eastern lobe, Hekla Ö and Aniakchak tephra were extended significantly eastwards, and the Hekla Y tephra was identified for the first time outside of Iceland. These results indicate that Icelandic tephra can travel to Finland along complex northerly and southerly pathways in addition to a direct eastwards dispersal route. Additionally, datasets of proximal geochemistry of Hekla X, Hekla Y, Hekla Z and Hekla 1845 tephras were produced and published to be used as an aid in establishing more robust correlations between the distal and proximal tephra records. The main outcome of this study is a first outline for a Finnish Holocene tephra framework. The high number of cryptotephra horizons in the framework demonstrates that there is great potential for further cryptotephra studies and utilization of tephrochronology as a dating method in Finland.Gjóskulagatímatal er nákvæm aldursgreiningaraðferð þar sem gjóskulög eru notuð til að tengja saman og tímasetja jarðlög og fornleifar. Gjóskulagatímatal á rætur að rekja til eldvirkra svæða jarðarinnar, en þaðan hefur aðferðin dreifst til fjarlægra svæða. Þróun aðferðarfræðinni hefur leitt til nýtingar smásærra gjósku (cryptotephra eða leynigjóska) sem hefur borist langt frá eldvirkum svæðum og myndar örþunn ósýnileg lög í jarðlögum. Í þessu doktorsverkefni er leitast við að kanna möguleika á notkun smásærrar gjósku til aldursgreininga í Finnlandi. Þessi rannsókn er fyrsta sinnar tegundar á smásærri gjósku í Finnlandi. Meginmarkmiðið með rannsókninni er að byggja upp gjóskulagatímatal í Finnlandi sem myndi nýtast sem aldursgreiningartæki í umhverfisrannsóknum í Fennóskandíu. Í verkefninu voru 30 mýrar og stöðuvötn í Suður- og Mið-Finnlandi könnuð með tilliti til tilvistar leynigjósku, og nær rannsóknarsvæðið frá Álandseyjum í vestri til landamæra Finnlands og Rússlands í austri. Niðurstöður rannsóknarinnar leiddu í ljós tilvist leynigjóskulaga frá 19 eldgosum, þar af voru 17 frá íslenskum eldstöðvum og tvö frá eldfjöllum í Alaska. Elsta efnagreinda gjóskan sem borist hefur til Finnlands er 7000 ára gömul Heklugjóska (Hekla 5), en yngsta gjóskan myndaðist hins vegar í Öskjugosinu árið 1875. Finnska gjóskulagatímatalið spannar því síðustu 7000 ár og niðurstöður verkefnisins sýna að gjóska hefur borist tiltölulega oft til Finnlands á þessu tímabili. Niðurstöður rannsóknarinnar sýna að mörg gjóskulög, eins og Askja 1875, Hekla 1845, Hekla 1510, Landnám (Torfajökull), White River Ash, Hekla Ö og Aniakchak hafa dreifst umtalsvert víðar enn áður hefur verið þekkt. Þar að auki er gjóskulaginu Hekla Y lýst í fyrsta sinn utan Íslands. Niðurstöður þessa verkefnis er mikilvægur grunnur að áframhaldandi rannsóknum á smásærri gjósku í Finnlandi, Fennóskandíu og vestur Evrópu. Sá fjöldi gjóskulaga sem fundist hefur í Finnlandi í þessari rannsókn gefur tilefni til og endurspeglar mikla möguleika á frekari gjóskurannsóknum og nýtingu gjóskulaga til að tímasetja jarðlög og umhverfisbreytingar í Finnlandi.Tefrokronologia on tarkka ajoitusmenetelmä, joka perustuu tefran eli tulivuoren tuhkan muodostamien kerrosten käyttöön arkeologisten ja geologisten ympäristöarkistojen ajoittamisessa ja korreloinnissa. Tefrokronologinen tutkimus on lähtöisin maapallon tuliperäisiltä seuduilta, joilta se on vähitellen levinnyt yhä kauemmaksi distaalialueille laboratorio- ja analyysimenetelmissä tapahtuneen kehityksen myötä. Nykyään ajoitushorisontteina on mahdollista käyttää jopa paljaalle silmälle näkymättömiä kerroksia, jotka muodostuvat kauimmaksi kantautuneista, mikroskooppisista vulkaanisen lasin partikkeleista eli kryptotefrasta. Tämän väitöskirjan päämääränä on arvioida tefrokronologian mahdollisuuksia Suomessa. Kryptotefran esiintymistä Suomessa ei ole aikaisemmin tutkittu, ja yksi työn tärkeimmistä tavoitteista oli luoda alueellinen tefrokronologinen kehys, jota voitaisiin käyttää ajoitustyökaluna suomalaisessa ympäristötutkimuksessa. Tutkimuskohteiksi valittiin 30 suota ja järveä, joista kryptotefraa etsittiin. Tutkimusalue kattaa koko Etelä- ja Keski-Suomen aina Ahvenanmaalta Venäjän rajalle saakka. Tutkimuskohteista löytyi kryptotefraa, joka on geokemiallisen koostumuksensa perusteella peräisin ainakin 17 islantilaisesta ja kahdesta alaskalaisesta tulivuorenpurkauksesta. Vanhin geokemiallisesti tunnistettu tuhkakerros on peräisin islantilaisen Hekla keskustulivuoren n. 7000 vuotta sitten tapahtuneesta purkauksesta, ja nuorin tuhkakerrostumista on kulkeutunut Suomeen islantilaisen Askja keskustulivuoren vuoden 1875 purkauksesta. Tämän tutkimuksen tuloksena rakennettu Suomen tefrokronologinen kehys kattaa siis noin 7000 vuotta, ja sen muodostavat tefrakerrostumat osoittavat, että tulivuoren tuhkaa on levinnyt Suomeen usein kyseisen ajanjakson aikana. Tulokset osoittavat myös, että useiden holoseenin tefrojen levinneisyysalueet ovat ulottuneet huomattavasti kauemmaksi itään kuin aiemmin on ollut tiedossa. Esimerkkejä tällaisista tefroista ovat Askja 1875, Hekla 1845, Hekla 1510, Landnám (Torfajökull), White River Ash, Hekla Ö sekä Aniakchak tefra. Lisäksi Hekla Y tefraa löytyi tämän tutkimuksen tuloksena ensimmäistä kertaa Islannin ulkopuolelta. Tulokset osoittavat, että tuhkapilvet kantautuvat Islannista Suomeen sekä suoraan lännestä että pitkin monimutkaisia pohjoisia ja eteläisiä kulkeutumisreittejä. Suomessa tehdyn kryptotefratutkimuksen lisäksi tässä väitöskirjatyössä tutkittiin Hekla X, Hekla Y, Hekla Z ja Hekla 1845 tefrojen geokemiallista koostumusta proksimaalialueiden geologisissa kerrostumissa. Uuden geokemiallisen datan avulla luotiin aiempaa luotettavampia yhteyksiä proksimaali- ja distaalialueiden tefrostratigrafioiden välille. Tämän väitöskirjan tärkein tulos on ensimmäisen suomalaisen tefrokronologisen kehyksen julkaisu. Kryptotefrahorisonttien suuri lukumäärä Suomessa osoittaa, että alueella on erinomaiset mahdollisuudet kryptotefroihin kohdistuvaan jatkotutkimukseen sekä tefrokronologian käyttämiseen ajoitusmenetelmänä.The Doctoral Programme in Biology, Geography and Geology at the University of Turku. Nordic Volcanological Center. Finnish Cultural Foundation, Varsinais-Suomi Regional Fund. Suomen Tiedeseura

Hekla 1947, 1845, 1510 and 1158 tephra in Finland: challenges of tracing tephra from moderate eruptions

Several cryptotephra layers that originate from Icelandic volcanic eruptions with a volcanic explosivity index (VEI) of 3 have previously been identified in Northern Europe, albeit within a restricted geographical area. One of these is the Hekla 1947 tephra that formed a visible fall-out in southern Finland. We searched for the Hekla 1947 tephra from peat archives within the previously inferred fall-out zone but found no evidence of its presence. Instead, we report the first identification of Hekla 1845 and Hekla 1510 cryptotephra layers outside of Iceland, the Faroe Islands, Ireland and the UK. Additionally, Hekla 1158 tephra was found in Finland for the first time. Our results confirm that Icelandic eruptions of moderate size can form cryptotephra deposits that are extensive enough to be used in inter-regional correlations of environmental archives and carry a great potential for refining regional tephrochronological frameworks. Our results also reveal that Icelandic tephra has been dispersed into Finnish airspace at least seven times during the past millennium and in addition to a direct eastward route the ash clouds can travel either via a northerly or a southerly transport pathway

Sediment trapping - An attempt to monitor temporal variation of microplastic flux rates in aquatic systems

Sediment trapping as a tool to monitor microplastic influx was tested in an urban boreal lake basin. The one-year-long trap monitoring consisted of 5-month and 7-month periods representing growing season and winter season (including the spring flood event), respectively. Sediment accumulation rate (SAR), and organic content were determined, highest SAR - 14.5 g/m(2)/d - was measured during the winter period. Microplastics were extracted from the sediment applying heavy-liquid density separation method and collected under a microscope for further identification with FTIR spectroscopy. PE was identified as the most abundant synthetic polymer type, while PP and PET are also present. The annual microplastic flux rate is 32 400 pieces/m2/ year, and highest accumulation does not coincide with the highest SAR, but occurs during the growing season. Changes in the microplastic accumulation rates are related to seasonal conditions. Highest microplastic concentration with respect to dry sediment weight (10 200 pieces/kg) was observed in a growing season sample, while highest concentration with respect to sediment volume (1800 pieces/l) was observed during winter. This finding underlines the problems related to reporting microplastic concentrations in various units. The results highlight that sediment trap monitoring is an efficient tool for monitoring microplastic accumulation rate in aquatic environments and provides an opportunity to better understand and define processes controlling microplastic accumulation. (C) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND licensePeer reviewe

Sediment trapping – An attempt to monitor temporal variation of microplastic flux rates in aquatic systems

ediment trapping as a tool to monitor microplastic influx was tested in an urban boreal lake basin. The one-year-long trap monitoring consisted of 5-month and 7-month periods representing growing season and winter season (including the spring flood event), respectively. Sediment accumulation rate (SAR), and organic content were determined, highest SAR – 14.5 g/m2/d – was measured during the winter period. Microplastics were extracted from the sediment applying heavy-liquid density separation method and collected under a microscope for further identification with FTIR spectroscopy. PE was identified as the most abundant synthetic polymer type, while PP and PET are also present. The annual microplastic flux rate is 32 400 pieces/m2/year, and highest accumulation does not coincide with the highest SAR, but occurs during the growing season. Changes in the microplastic accumulation rates are related to seasonal conditions. Highest microplastic concentration with respect to dry sediment weight (10 200 pieces/kg) was observed in a growing season sample, while highest concentration with respect to sediment volume (1800 pieces/l) was observed during winter. This finding underlines the problems related to reporting microplastic concentrations in various units. The results highlight that sediment trap monitoring is an efficient tool for monitoring microplastic accumulation rate in aquatic environments and provides an opportunity to better understand and define processes controlling microplastic accumulation.</p

Sediment trapping as a method for monitoring microplastic flux rates and deposition at aquatic environments

Microplastics are reported from wide range of aquatic environments with concentrations up to thousands of particles per kilogram of sediment. Due to a lack of temporal control, evaluation of the influx rate of microplastic pollution is not enabled. However, understanding the annual flux rate of microplastics to the aquatic environments is a crucial aspect for environmental monitoring and for risk assessment. A sediment trap method is widely applied in aquatic sedimentary studies in order to measure sedimentation rates and understand sedimentation processes. We have tested near-bottom sediment trap method in lacustrine and estuary environments, at central and coastal Finland, for measuring and quantifying the microplastic influx rate during one year. Near-bottom sediment traps with two collector tubes and known surface area, fixed one meter from the bottom, collect all particles that are about to accumulate on the basin floor of the water body. Controlled temporal interval of trap maintenance enables calculation and determination of local microplastic influx rate i.e. number of accumulating particles per time per surface area. The test results are very promising. Near-bottom sediment traps can be used for long term monitoring in order to gain a deeper understanding of the microplastic transport and sedimentation processes, confirm and compare the feasibility and efficiency of different environmental conservation methods, setting threshold values for microplastic influx, and supervising that the defined target conditions are met.</p

An outline for Finnish tephrochronology – Volcanic ash as a dating method in Finland

Tephrochronology is a high-precision dating method that uses volcanic ash horizons as isochrons in correlating and dating geological records and archaeological sites. First developed in the volcanic regions of the world, tephrochronology has expanded to ever more distal areas with improved laboratory and analytical methods that have enabled the utilization of even the scarcest deposits of far-travelled cryptotephra i.e. small volcanic glass shards that are invisible to the naked eye. The objective of this dissertation is to assess the potential of cryptotephra studies and tephrochronology in Finland. No cryptotephra studies had been conducted in Finland previously, and the ultimate aim of the work presented here was to establish a first outline for a Finnish tephrochronology that could be used as a dating tool in environmental research in the region. Cryptotephra was searched from 30 peatland and lake sites from an area that covers the whole southern and central Finland from Åland archipelago in the west to the Russian border in the east. As a result, cryptotephra deposits from at least 17 Icelandic and two Alaskan volcanic eruptions were detected and geochemically characterized from the Finnish environmental archives. The oldest identified tephra in Finland is the 7 ka Hekla 5 tephra and the youngest one is the Askja 1875 tephra. The Finnish tephrochronology therefore covers approximately 7000 years and the results of this study demonstrate that dispersal of tephra to Finland has been relatively frequent throughout this time. Within this project, the known dispersal areas of several Holocene tephras, such as Askja 1875, Hekla 1845, Hekla 1510, Landnám (Torfajökull), White River Ash eastern lobe, Hekla Ö and Aniakchak tephra were extended significantly eastwards, and the Hekla Y tephra was identified for the first time outside of Iceland. These results indicate that Icelandic tephra can travel to Finland along complex northerly and southerly pathways in addition to a direct eastwards dispersal route. Additionally, datasets of proximal geochemistry of Hekla X, Hekla Y, Hekla Z and Hekla 1845 tephras were produced and published to be used as an aid in establishing more robust correlations between the distal and proximal tephra records. The main outcome of this study is a first outline for a Finnish Holocene tephra framework. The high number of cryptotephra horizons in the framework demonstrates that there is great potential for further cryptotephra studies and utilization of tephrochronology as a dating method in Finland.Tefrokronologia on tarkka ajoitusmenetelmä, joka perustuu tefran eli tulivuoren tuhkan muodostamien kerrosten käyttöön arkeologisten ja geologisten ympäristöarkistojen ajoittamisessa ja korreloinnissa. Tefrokronologinen tutkimus on lähtöisin maapallon tuliperäisiltä seuduilta, joilta se on vähitellen levinnyt yhä kauemmaksi distaalialueille laboratorio- ja analyysimenetelmissä tapahtuneen kehityksen myötä. Nykyään ajoitushorisontteina on mahdollista käyttää jopa paljaalle silmälle näkymättömiä kerroksia, jotka muodostuvat kauimmaksi kantautuneista, mikroskooppisista vulkaanisen lasin partikkeleista eli kryptotefrasta. Tämän väitöskirjan päämääränä on arvioida tefrokronologian mahdollisuuksia Suomessa. Kryptotefran esiintymistä Suomessa ei ole aikaisemmin tutkittu, ja yksi työn tärkeimmistä tavoitteista oli luoda alueellinen tefrokronologinen kehys, jota voitaisiin käyttää ajoitustyökaluna suomalaisessa ympäristötutkimuksessa. Tutkimuskohteiksi valittiin 30 suota ja järveä, joista kryptotefraa etsittiin. Tutkimusalue kattaa koko Etelä- ja Keski-Suomen aina Ahvenanmaalta Venäjän rajalle saakka. Tutkimuskohteista löytyi kryptotefraa, joka on geokemiallisen koostumuksensa perusteella peräisin ainakin 17 islantilaisesta ja kahdesta alaskalaisesta tulivuorenpurkauksesta. Vanhin geokemiallisesti tunnistettu tuhkakerros on peräisin islantilaisen Hekla keskustulivuoren n. 7000 vuotta sitten tapahtuneesta purkauksesta, ja nuorin tuhkakerrostumista on kulkeutunut Suomeen islantilaisen Askja keskustulivuoren vuoden 1875 purkauksesta. Tämän tutkimuksen tuloksena rakennettu Suomen tefrokronologinen kehys kattaa siis noin 7000 vuotta, ja sen muodostavat tefrakerrostumat osoittavat, että tulivuoren tuhkaa on levinnyt Suomeen usein kyseisen ajanjakson aikana. Tulokset osoittavat myös, että useiden holoseenin tefrojen levinneisyysalueet ovat ulottuneet huomattavasti kauemmaksi itään kuin aiemmin on ollut tiedossa. Esimerkkejä tällaisista tefroista ovat Askja 1875, Hekla 1845, Hekla 1510, Landnám (Torfajökull), White River Ash, Hekla Ö sekä Aniakchak tefra. Lisäksi Hekla Y tefraa löytyi tämän tutkimuksen tuloksena ensimmäistä kertaa Islannin ulkopuolelta. Tulokset osoittavat, että tuhkapilvet kantautuvat Islannista Suomeen sekä suoraan lännestä että pitkin monimutkaisia pohjoisia ja eteläisiä kulkeutumisreittejä. Suomessa tehdyn kryptotefratutkimuksen lisäksi tässä väitöskirjatyössä tutkittiin Hekla X, Hekla Y, Hekla Z ja Hekla 1845 tefrojen geokemiallista koostumusta proksimaalialueiden geologisissa kerrostumissa. Uuden geokemiallisen datan avulla luotiin aiempaa luotettavampia yhteyksiä proksimaali- ja distaalialueiden tefrostratigrafioiden välille. Tämän väitöskirjan tärkein tulos on ensimmäisen suomalaisen tefrokronologisen kehyksen julkaisu. Kryptotefrahorisonttien suuri lukumäärä Suomessa osoittaa, että alueella on erinomaiset mahdollisuudet kryptotefroihin kohdistuvaan jatkotutkimukseen sekä tefrokronologian käyttämiseen ajoitusmenetelmänä

Vedde Ash constrains Younger Dryas glacier re-advance and rapid glacio-isostatic rebound on Svalbard

The distal deposition of tephra from explosive volcanism has the potential to geochronologically constrain sedimentary archives and landforms. With this technique, we constrain a Late Glacial glacier re-advance on Svalbard and suggest that glacioisostatic emergence rates during the Younger Dryas chronozone were at least three times greater than previous estimates. The identification of cryptotephra (i.e., non-visible) horizons, outside the extent of visible fallout, has greatly expanded the field of application of tephrochronology. While the cryptotephra revolution has triggered a burst of investigations using low-concentration tephra to constrain distal sedimentary sequences, as of yet, few investigations have used this tool to constrain the age of glacial landforms. Here we constrain a moraine formed during a glacier re-advance (12.8–12.2 cal ka BP) into a high relative sea level during the early Younger Dryas chronozone, with the first identified occurrence of the Icelandic Vedde Ash on Svalbard. Low concentrations (∼63 shards/g dried sediment) of the bimodal Vedde Ash (rhyolitic long axis c. 30–90 μm; basaltic c. 35–100 μm) were identified in a lake sediment sequence collected from the Heftyebreen glacier foreland, in a tributary valley to Grønfjorden, western Spitsbergen. Given that the cryptotephra was deposited within a lacustrine isolation basin, we further reconstruct a minimum rate of glacio-isostatic emergence during the end of the Late Glacial. Strong and longstanding evidence suggests Svalbard's west-coast cirque glaciers were less extensive during the Late Glacial than the Late Holocene. However, the Late Glacial Heftyebreen moraine suggests Svalbard glacier dynamics during this period may have been more complex

Rapid shifting of a deep magmatic source at Fagradalsfjall volcano, Iceland

AbstractRecent Icelandic rifting events have illuminated the roles of centralized crustal magma reservoirs and lateral magma transport1–4, important characteristics of mid-ocean ridge magmatism1,5. A consequence of such shallow crustal processing of magmas4,5 is the overprinting of signatures that trace the origin, evolution and transport of melts in the uppermost mantle and lowermost crust6,7. Here we present unique insights into processes occurring in this zone from integrated petrologic and geochemical studies of the 2021 Fagradalsfjall eruption on the Reykjanes Peninsula in Iceland. Geochemical analyses of basalts erupted during the first 50 days of the eruption, combined with associated gas emissions, reveal direct sourcing from a near-Moho magma storage zone. Geochemical proxies, which signify different mantle compositions and melting conditions, changed at a rate unparalleled for individual basaltic eruptions globally. Initially, the erupted lava was dominated by melts sourced from the shallowest mantle but over the following three weeks became increasingly dominated by magmas generated at a greater depth. This exceptionally rapid trend in erupted compositions provides an unprecedented temporal record of magma mixing that filters the mantle signal, consistent with processing in near-Moho melt lenses containing 107–108 m3 of basaltic magma. Exposing previously inaccessible parts of this key magma processing zone to near-real-time investigations provides new insights into the timescales and operational mode of basaltic magma systems.</jats:p