Physical Characteristics of Thingvallavatn, Iceland

Aðalsteinsson, Hákon; Jónasson, Pétur M.; Rist, Sigurjón

doi:10.2307/3545048

Cited by 30 publications

(24 citation statements)

References 16 publications

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“…Growth at low salinity did not evolve to become increasingly developmentally unresponsive to salinity even after many thousands of generations in the constant low-salinity environment of Icelandic lakes [71]. The absence of any genetic assimilation of growth in lake stickleback in Iceland contrasts with that of freshwater demes from the St Laurence estuary which have reduced plasticity compared with local saltwater demes [65].…”

Section: Discussionmentioning

confidence: 69%

Evolution of growth by genetic accommodation in Icelandic freshwater stickleback

Robinson

2013

Proc. R. Soc. B.

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Classical Darwinian adaptation to a change in environment can ensue when selection favours beneficial genetic variation. How plastic trait responses to new conditions affect this process depends on how plasticity reveals to selection the influence of genotype on phenotype. Genetic accommodation theory predicts that evolutionary rate may sharply increase when a new environment induces plastic responses and selects on sufficient genetic variation in those responses to produce an immediate evolutionary response, but natural examples are rare. In Iceland, marine threespine stickleback that have colonized freshwater habitats have evolved more rapid individual growth. Heritable variation in growth is greater for marine full-siblings reared at low versus high salinity, and genetic variation exists in plastic growth responses to low salinity. In fish from recently founded freshwater populations reared at low salinity, the plastic response was strongly correlated with growth. Plasticity and growth were not correlated in full-siblings reared at high salinity nor in marine fish at either salinity. In well-adapted lake populations, rapid growth evolved jointly with stronger plastic responses to low salinity and the persistence of strong plastic responses indicates that growth is not genetically assimilated. Thus, beneficial plastic growth responses to low salinity have both guided and evolved along with rapid growth as stickleback adapted to freshwater.

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Section: Discussionmentioning

confidence: 69%

Evolution of growth by genetic accommodation in Icelandic freshwater stickleback

Robinson

2013

Proc. R. Soc. B.

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“…The lake is approximately 90 % spring-fed (Adalsteinsson et al, 1992) and so there is very little surface inflow of sediments. Hence, sedimentation within the lake is dominantly from biogenic activity with minor wind-blown dust and volcanic particles.…”

Section: Geological Backgroundmentioning

confidence: 99%

Magmatic and tectonic history of Iceland's western rift zone at Lake Thingvallavatn

Bull

Minshull

Mitchell

et al. 2005

Geol Soc America Bull

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High rates of Holocene sedimentation in a lake spanning the Thingvellir rift zone of western Iceland provide an unusual opportunity to study the interaction of tectonic and magmatic processes on timescales of thousands of years. Lake Thingvallavatn is oriented SW-NE, parallel to the trend of normal faults and fissures which extend northeast from Hengill, a central volcano system. Thingvallavatn's lake sediments provide a continuous high-fidelity record of tectono-magmatic processes. "Chirp" sub-bottom profiler and sidescan records, together with sediment core information, enabled the lake stratigraphy to be constrained well since the emplacement of a post-glacial lava at 9.1 ± 0.3 ka. This lava, together with three younger horizons, enabled detailed study of the main tectonic and magmatic events. A major Hengill volcanic event which controlled the development of the present-day lake morphology occurred at 1.9 ka with the eruption of a scoria cone within the lake (Sandey). During this event, the Nesjahraun lava was erupted into the southern part of the lake, the Sandey scoria cone was formed, and major faulting and subsidence occurred in the northern part of the lake, resulting in the formation of an asymmetrical rift. Within the southern part of the lake, a deformed sequence of sediments of age 2.9 -1.5 ka, between undeformed younger and older sediments, indicate that liquefaction phenomena are associated with the emplacement of the Nesjahraun lava. Analysis of fault displacement reveals that the total throw summed over all faults across the width of the rift zone is approximately constant (110 -130 m) along the long axis of the rift. We estimate an extension rate on the faults of 3.3 -8.2 mm yr -1 since 9.1 ka, assuming fault dips of 60 -75°, which represents 17 -1 43 % of the total plate boundary extension estimated from global plate motion inversion. We speculate that the remaining extension must either be taken up elsewhere in Iceland, for example in the Eastern Rift Zone or along the South Island Seismic Zone, or that extension estimated over the last 9kyr underestimates the long-term extension rate due to incomplete sampling of the episodic magmatic component.

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“…During winter months, the main body of Lake Thingvallavatn is generally isothermal between 0.8-1.4°C. Source water of the Silfra inflow percolates through the underlying rock and has historically been found to have a near-constant, year-round temperature (*3.3°C) and conductivity (*71 lS cm -1 ) (Adalsteinsson et al 1992). This inflow conductivity is very close to that of the ambient lake water of (65-70 lS cm -1 ) (Lindegaard 1992) and as such salinity will not significantly affect density.…”

Section: Methodsmentioning

confidence: 64%

Section: Methodsmentioning

confidence: 99%

“…1-filled star), and a total volume of 2.9 km 3 (Adalsteinsson et al 1992). From 1951From -1990, Lake Thingvallavatn was predictably ice-covered from January through April (Adalsteinsson et al 1992). In the winters of 2002-2008, ice cover has demonstrated large spatial and temporal variability during the 5-week average frozen period; for two of these years, Lake Thingvallavatn was observed to be ice-free (Sveinbjornsson 2009).…”

Section: Methodsmentioning

confidence: 99%

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Preconditioning of an underflow during ice-breakup in a subarctic lake

2011

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The fate of inflows into lakes has been extensively studied during summer stratification but has seen relatively little focus during the weak winter stratification, with or without ice-cover. Field observations are presented of groundwater inflow into a shallow bay of a subarctic lake. Atmospheric forcing of the bay during the study period was extremely variable and coincided with spring ice-cover break-up. Two dominant wind regimes were identified; (1) weak wind-forcing (wind speed \5 m s -1 or land-fast ice-cover), and (2) strong wind-forcing (wind speed [5 m s -1 and open water). At a relatively constant temperature of *3.3°C, the groundwater inflow was closer to the temperature of maximum density than the water in the main body of the lake, which during the observed winter stratification is *1.2°C. During weak wind-forcing, the stratification within Silfra Bay approximated two-layers as this denser groundwater formed a negatively buoyant underflow. A calculated underflow entrainment rate of 2.8 9 10 -3 agrees well with other underflow studies. During strong wind-forcing, the water column out to the mouth of the bay became weakly stratified as the underflow was entrained vertically by wind-stirring. Observed periods of mixing can be predicted to occur when turbulent kinetic energy (TKE) production by wind stirring integrated over the underflow hydraulic residence time in the bay exceeds the potential energy associated with the stratification. A decrease of ice cover, as observed in the studied subarctic lake over the last decade, will result in the underflow being more frequently exposed to the strong wind-forcing regime during winter, thereby altering the winter distribution of groundwater inflow within the lake.

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Physical Characteristics of Thingvallavatn, Iceland

Cited by 30 publications

References 16 publications

Evolution of growth by genetic accommodation in Icelandic freshwater stickleback

Evolution of growth by genetic accommodation in Icelandic freshwater stickleback

Magmatic and tectonic history of Iceland's western rift zone at Lake Thingvallavatn

Preconditioning of an underflow during ice-breakup in a subarctic lake

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