TY - JOUR

T1 - The fate of the submarine ikaite tufa columns in southwest Greenland under changing climate conditions.

AU - Hansen, Marc O.

AU - Buchardt, Bjørn

AU - Kühl, Michael

AU - Elberling, Bo

PY - 2011

Y1 - 2011

N2 - Ikaite is considered a metastable mineral forming and stable only at low temperatures and therefore an indicatorof low-temperature carbonate precipitation often associated with cold marine seeps. It is found world-wide but mostspectacularly in Ikka Fjord in southwest Greenland as submarine carbonate tufa columns. Here, ikaite is formed as a result ofsubmarine spring water mixing with cold seawater. As ikaite disintegrates at temperatures above 6–7uC, it has been speculatedthat global warming could endanger this unique habitat as well as other sites. In Ikka Fjord in situ water chemistry in andaround an ikaite column measured continuously over two years showed that the column water is alkaline (pH . 9–10)throughout the year with temperatures of 21.3–6.0 uC and conductivities of 5.7–7.9 mS cm21, favoring year-round growth ofcolumns at 4–5 cm per month. Short-term in situ measurements with needle micro sensors from both older dehydrated andcalcified parts and more recently formed solid parts of an ikaite tufa column showed similar pH and temperature values,including a temperature variation over the tidal cycle. In the uppermost, recently deposited ikaite matrix, spring water escapingat the top causes passive drag of seawater into the porous ikaite matrix, leading to a mixing layer several centimeters thick thathas pH values intermediate to the spring water in the column and the surrounding seawater. We conclude that the main part ofthe columns, consisting of fossilized ikaite (inverted to calcite) partly sealed by calcifying coralline algae and with year-roundflow of alkaline freshwater through distinct channels, are resistant to warming. In the more diffuse top part of the columns, theformation of ikaite, and thus column growth, will be limited in the future due to increased fjord water temperature during the, 3 summer months a year

AB - Ikaite is considered a metastable mineral forming and stable only at low temperatures and therefore an indicatorof low-temperature carbonate precipitation often associated with cold marine seeps. It is found world-wide but mostspectacularly in Ikka Fjord in southwest Greenland as submarine carbonate tufa columns. Here, ikaite is formed as a result ofsubmarine spring water mixing with cold seawater. As ikaite disintegrates at temperatures above 6–7uC, it has been speculatedthat global warming could endanger this unique habitat as well as other sites. In Ikka Fjord in situ water chemistry in andaround an ikaite column measured continuously over two years showed that the column water is alkaline (pH . 9–10)throughout the year with temperatures of 21.3–6.0 uC and conductivities of 5.7–7.9 mS cm21, favoring year-round growth ofcolumns at 4–5 cm per month. Short-term in situ measurements with needle micro sensors from both older dehydrated andcalcified parts and more recently formed solid parts of an ikaite tufa column showed similar pH and temperature values,including a temperature variation over the tidal cycle. In the uppermost, recently deposited ikaite matrix, spring water escapingat the top causes passive drag of seawater into the porous ikaite matrix, leading to a mixing layer several centimeters thick thathas pH values intermediate to the spring water in the column and the surrounding seawater. We conclude that the main part ofthe columns, consisting of fossilized ikaite (inverted to calcite) partly sealed by calcifying coralline algae and with year-roundflow of alkaline freshwater through distinct channels, are resistant to warming. In the more diffuse top part of the columns, theformation of ikaite, and thus column growth, will be limited in the future due to increased fjord water temperature during the, 3 summer months a year

U2 - 10.2110/jsr.2011.50

DO - 10.2110/jsr.2011.50

M3 - Journal article

VL - 81

SP - 553

EP - 561

JO - Journal of Sedimentary Research

JF - Journal of Sedimentary Research

SN - 1527-1404

IS - 8

ER -