Marine System Analysis Group

Byfjord status March 2012

Daniel Hansson — Tue, 27 Mar 2012 13:52:15 +0000

Vattenprofil för Byfjorden den 26 mars 2012. Bilden visar temperatur (röd), salthalt (svart) och syrekoncentration (blå) från ytan till cirka 45 meters djup. Den streckade linjen visar en mätning utförd den 18 januari 2012. Klicka på bilden för större version.

Under februari var Byfjorden täckt med is, varför ingen uppdatering gjordes då. Mars månads mätning genomfördes den 26 mars 2012.

Resultatet från mätningen visar att de senaste dagarnas varma temperaturer snabbt värmt upp ytlagret. De översta metrarna har en temperatur på cirka 6 grader, men under finns betydligt kallare vatten. Även djupvattnet har blivit kallare sedan januari, främst på grund av inflödet som skedde runt nyår (pumparna har varit avstängda sedan januari).

Salthalten har, som en följd av inflödet, ökat något i djupvattnet.

Syrekoncentrationerna har ökat över tröskeldjup. Det beror på att kallare vatten, som det var under vintern, löser mer syre än varmare vatten. Under tröskeldjup minskar syrehalterna däremot snabbt. Det är fortfarande syresatt på alla djup, men under 40 m kommer det snart att saknas syre. Gränsen för syrebrist ligger på cirka 35 m. Eftersom pumparna har varit avstängda sedan i januari har inget nytt syre tillsatts sedan dess.

Byfjord status in January 2012

Daniel Hansson — Thu, 19 Jan 2012 11:36:33 +0000

Vattenprofil för Byfjorden den 18 januari 2012. Bilden visar temperatur (röd), salthalt (svart) och syrekoncentration (blå) från ytan till cirka 45 meters djup. Den streckade linjen visar en mätning utförd den 19 december 2011. Klicka på bilden för större version.

An inflow event commenced around christmas time and is still ongoing. It has affected the Byfjord in several ways.

Only small changes have occured in the surface layer since December. This is due to more or less similar meteorological conditions over the past month. In the deepwater, however, temperature has decreased by about 2 degrees Celsius as the inflowing water has a lower temperature.

Deepwater salinity has increased, but decreased below 37 m. This is an effect of a dense bottom current, created by inflowing water. The water ventilates the whole water volume of the deepwater, and the current erode the secondary halocline below the pump outlet. Integrated over the whole deepwater column, the salinity has increased by 0.3 units over the past month.

Over the past month, large amounts of oxygenated water has flowed into the basin. Hypoxia only remain at the layer closest to the sea bed. The sediment has a high oxygen debt, and the supplied oxygen quickly diminishes as the debt is repaid.

Byfjord status in December 2011

Daniel Hansson — Tue, 20 Dec 2011 08:55:55 +0000

Vattenprofil för Byfjorden den 19 december 2011. Bilden visar temperatur (röd), salthalt (svart) och syrekoncentration (blå) från ytan till cirka 45 meters djup. Den streckade linjen visar en mätning utförd den 15 november 2011. Klicka på bilden för större version.

Berit, the storm that thrashed Scandinavia in late November, homogenised Byfjord’s surface layer. The temperuater decresed by about 3 degrees and the salinity decreased as freshwater from the surface was mixed into the water column. For the deepwater, storms such as these do not improve the oxygen concentrations as sea level within Byfjord is to high.

The pumps have continued to freshedn the deepwater. Since mid November, about 0.8 salinity units has been removed. The increasingly cold surface water, that is pumped down, has also decresed the average deepwater temperature by about 0.5 degrees C.

Oxygen consumption is lower in winter than the rest of the year. Thus, more of the added oxygen is left in the deepwater. A steady, but small, increase in oxygen concentrations has been observed over the past month.

Byfjord status in November 2011

Daniel Hansson — Wed, 16 Nov 2011 09:32:58 +0000

Vattenprofil för Byfjorden den 15 november 2011. Bilden visar temperatur (röd), salthalt (svart) och syrekoncentration (blå) från ytan till cirka 45 meters djup. Den streckade linjen visar en mätning utförd den 18 oktober 2011. Klicka på bilden för större version.

Over the past month, the pumps have reduced the deep-water salinity after an inflow in October. The average salinity below sill depth is 27.5, which is a few tenths lower than in October.

Oxygen concentrations are increasing in the upper part of the deep-water, but remain low at the pump outlet depth. However, hydrogen sulphide is only present at 40 m and deeper. Surface water are showing increasing oxygen concentrations due to decreasing air temperatures. This means colder water that have the ability to dissolve more oxygen.

Byfjord status in October 2011

Daniel Hansson — Thu, 20 Oct 2011 07:44:17 +0000

Vattenprofil för Byfjorden den 18 oktober 2011. Bilden visar temperatur (röd), salthalt (svart) och syrekoncentration (blå) från ytan till cirka 45 meters djup. Den streckade linjen visar en mätning utförd den 20 september 2011. Klicka på bilden för större version.

An inflow occurred in mid-October. The inflowing water was old deep-water from Havstensfjord. This water was lifted up and over the Sunningen sill due to ventilation of the upper deep-water in Havstensfjord. The inflowing water was warmer, saltier and poorer oxygenated than the water in the Byfjord basin. The temperature increased from 9 to 11 degrees Celsius, salinity increased by 2 units in the deeper part of the deep-water and the oxygen concentrations decreased slightly.

Byfjord status in September 2011

Daniel Hansson — Fri, 30 Sep 2011 08:19:46 +0000

Vattenprofil för Byfjorden den 20 september 2011. Bilden visar temperatur (röd), salthalt (svart) och syrekoncentration (blå) från ytan till cirka 45 meters djup. Den streckade linjen visar en mätning utförd den 16 augusti 2011. Klicka på bilden för större version.

Colder air temperatures cool the Byfjord surface. Since August, the water temperature in the top most 10 metres has decreased by almost 5 degrees Celsius. Meanwhile, summer water has been mixed further down into the water column, showing as increasing temperatures at sill depth. The deep-water temperature is also increasing. Over the past month the increase amounts to about 1 degree Celsius.

Precipitation and large amounts of river runoff has decreased the basin salinity. Beneath sill depth, the salinity reduction is 0.8 since August. Since October 2010, when the pumps were first switched on, the salinity in the deep-water has decreased by 3 salinity units.

Oxygen concentrations are normal for the surface layer, but improving at 10 to 15 metres depth due to intermediate water inflows. Below sill depth, oxygen concentrations remain at about 45 umol O2 per litre water (corresponding to approx. 1 ml O2 per litre). The oxygen supply is balanced almost exactly by the oxygen consumption. Higher oxygen concentrations can be expected when the wind turns from westerly to easterly, allowing ventilation of the deep-water.

Byfjord status in August 2011

Daniel Hansson — Wed, 17 Aug 2011 08:54:08 +0000

Vattenprofil för Byfjorden den 16 augusti 2011. Bilden visar temperatur (röd), salthalt (svart) och syrekoncentration (blå) från ytan till cirka 45 meters djup. Den streckade linjen visar en mätning utförd den 19 juli 2011. Klicka på bilden för större version.

The Byfjord was profiled on 16 August 2011. Over the past month, temperature had increased by approximately 1 degree Celsius beneath sill level. Salinity had also reduced about one salinity unit. Oxygen concentrations were still low, but higher than normal for the system.

Over the first half of August, biofouling has affected the top most oxygen optode at the mooring, continuously measuring oxygen concentrations in the fjord. This resulted in extremely low oxygen concentrations beeing measured at 2 m depth in the Byfjord. When the instrument was picked up and cleaned, then redeployed, oxygen concentrations returned to normal levels.

Biofouling cause significantly lower oxygen concentrations to be measured. When cleaned, the oxygen concentrations returned to normal.

Byfjord status in July 2011

Daniel Hansson — Wed, 20 Jul 2011 10:32:46 +0000

Vattenprofil för Byfjorden den 19 juli 2011. Bilden visar temperatur (röd), salthalt (svart) och syrekoncentration (blå) från ytan till cirka 45 meters djup. Den streckade linjen visar en mätning utförd den 16 juni 2011. Klicka på bilden för större version.

On 19 July, the water temperature in the surface water of Byfjord was almost 20 degrees Celsius, slightly colder than the same time last year. Secchi depth was about 5 metres, which is quite deep for this fjord. Meanwhile, the salinity has been reduced in the deepwater due to pumping activities. Oxygen conditions have been improved in the deepest part of the deepwater, but somewhat lower around sill level.

Two weeks after pumpstart

Daniel Hansson — Fri, 01 Jul 2011 14:07:55 +0000

Comparison of profiles 16 June and 28 June 2011. Red shows temperature, black is salinity and blue denotes oxygen concentrations. Solid line show profile from 28 June 2011 and dashed line shows the profile from 16 June 2011. Click on image for a larger version.

The Byfjord pumps went offline in late winter due to technical reasons. Severe ice conditions was not an easy match for the pumps or tubes. However, on 16 June the renovation was completed and the pumps restarted. During the last week, some profiles were taken of the water column showing that the pumps have already had a large impact on the fjord. After only two weeks the deep-water has become slightly colder due to sinking intermediate water from sill depth. The salinity has also been reduced from approximately 35 m up to sill depth. Oxygen concentrations have also been improved in the deepest parts of the fjord.

The changes are exactly what can be expected from pumping. The halocline at sill depth has evolved and a larger gradient between surface and deep-water is now found. A secondary pycnocline can be seen at the depth where pumped water is released, approximately at 35 meters depth. If the pumps continue to work without problems they will add even more oxygen to the deep-water and the density will be reduced. This increased the chances of new oxygenated water from outside the sill to flow into the basin and renew the resident water.

Byfjord status in May 2011

Daniel Hansson — Tue, 21 Jun 2011 11:34:29 +0000

Vattenprofil för Byfjorden den 16 juni 2011. Bilden visar temperatur (röd), salthalt (svart) och syrekoncentration (blå) från ytan till cirka 45 meters djup. Den streckade linjen visar en mätning utförd den 18 maj 2011. Klicka på bilden för större version.

Over the past month, only very small changes have occured in the Byfjord. The water temperature at the surface is about 18 degress Celsius and the salinity has decreased slightly since May. Beneath sill level the temperature and salinity levels remain constant. Oxygen concentrations have continued to decrease as it is consumed by decaying organic matter. The pumps were restarted the same date as the profile was take. Hopefully this means that we will see increasing oxygen concentrations again in the months to come.