Salinity and hypoxia in the Baltic Sea since A.D. 1500

Hansson, Daniel; Gustafsson, Erik

doi:10.1029/2010jc006676

Cited by 23 publications

(20 citation statements)

References 28 publications

(52 reference statements)

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“…For instance, changes in stratification have an impact on oxygen concentrations in the deep. Oxygen conditions improve in the deep due to a better ventilation initiated by reduced salinity (Hansson and Gustafsson, 2011) or higher wind speed (Meier et al, 2012a). These factors counteract the oxygen reduction in RCO-MCA and in our sensitivity studies.…”

Section: Discussionsupporting

confidence: 56%

“…Following their argumentation, salinity and temperature anomalies cannot explain hypoxia during the MCA. Therefore, it resulted from anthropogenic impacts (Zillén et al, 2008;Zillén and Conley, 2010) similarly to the 20th century (Conley et al, 2009;Hansson and Gustafsson, 2011;Gustafsson et al, 2012). However, historical nutrient loads are not estimated yet and the effect of pure natural climate change during the MCA has not been investigated so far.…”

Section: Introductionmentioning

confidence: 99%

“…Baltic Sea ocean model studies of the period before 1900 are very rare until today. Hansson and Gustafsson (2011) used the PROBE-Baltic ocean model to simulate Baltic Sea conditions during the last 500 yr. Their results indicate a strong decrease of bottom oxygen only after 1950 with no significant signals before including the LIA. They suggest that increased nutrient inputs most likely dominate the expansion of hypoxic bottom areas during the last century.…”

Section: Introductionmentioning

confidence: 99%

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The climate in the Baltic Sea region during the last millennium simulated with a regional climate model

et al. 2012

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Abstract. Variability and long-term climate change in the Baltic Sea region is investigated for the pre-industrial period of the last millennium. For the first time dynamical downscaling covering the complete millennium is conducted with a regional climate model in this area. As a result of changing external forcing conditions, the model simulation shows warm conditions in the first centuries followed by a gradual cooling until ca. 1700 before temperature increases in the last centuries. This long-term evolution, with a Medieval Climate Anomaly (MCA) and a Little Ice Age (LIA), is in broad agreement with proxy-based reconstructions. However, the timing of warm and cold events is not captured at all times. We show that the regional response to the global climate anomalies is to a strong degree modified by the large-scale circulation in the model. In particular, we find that a positive phase of the North Atlantic Oscillation (NAO) simulated during MCA contributes to enhancing winter temperatures and precipitation in the region while a negative NAO index in the LIA reduces them. In a second step, the regional ocean model (RCO-SCOBI) is used to investigate the impact of atmospheric changes onto the Baltic Sea for two 100 yr time slices representing the MCA and the LIA. Besides the warming of the Baltic Sea, the water becomes fresher at all levels during the MCA. This is induced by increased runoff and stronger westerly winds. Moreover, the oxygen concentrations in the deep layers are slightly reduced during the MCA. Additional sensitivity studies are conducted to investigate the impact of even higher temperatures and increased nutrient loads. The presented experiments suggest that changing nutrient loads may be more important determining oxygen depletion than changes in temperature or dynamic feedbacks.

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Section: Discussionsupporting

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The climate in the Baltic Sea region during the last millennium simulated with a regional climate model

et al. 2012

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“…This can be exemplified by the spread of anoxic bottom water in coastal seas, which is closely linked to both riverine nutrient load and stagnation periods (e.g. Hansson and Gustafsson, 2011). Changes due to deoxygenation, marine acidification and climate change may have severe implications for carbon and nutrient cycles, as well as for marine ecosystems.…”

Section: Introductionmentioning

confidence: 99%

Future changes in the Baltic Sea acid–base (pH) and oxygen balances

Omstedt¹,

Edman

Claremar³

et al. 2012

Tellus B: Chemical and Physical Meteorology

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A B S T R A C T Possible future changes in Baltic Sea acidÁbase (pH) and oxygen balances were studied using a catchmentÁsea coupled model system and numerical experiments based on meteorological and hydrological forcing datasets and scenarios. By using objective statistical methods, climate runs for present climate conditions were examined and evaluated using Baltic Sea modelling. The results indicate that increased nutrient loads will not inhibit future Baltic Sea acidification; instead, the seasonal pH cycle will be amplified by increased biological production and mineralization. All examined scenarios indicate future acidification of the whole Baltic Sea that is insensitive to the chosen global climate model. The main factor controlling the direction and magnitude of future pH changes is atmospheric CO 2 concentration (i.e. emissions). Climate change and land-derived changes (e.g. nutrient loads) affect acidification mainly by altering the seasonal cycle and deep-water conditions. Apart from decreasing pH, we also project a decreased saturation state of calcium carbonate, decreased respiration index and increasing hypoxic area Á all factors that will threaten the marine ecosystem. We demonstrate that substantial reductions in fossil-fuel burning are needed to minimise the coming pH decrease and that substantial reductions in nutrient loads are needed to reduce the coming increase in hypoxic and anoxic waters.

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“…Reconstructing annual mean salinities since 1500 (Hansson and Gustafsson 2011) indicates that salinity has slowly increased by 0.5 g kg −1 since 1500, peaking in the mid-eighteenth century. Present salinity values are nearly as high as reconstructed for the earlier maximum salinity period.…”

Section: 3mentioning

confidence: 99%

Recent Change—Marine Circulation and Stratification

Elken

Lehmann

Myrberg

2015

Regional Climate Studies

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This chapter describes recent change in the circulation and stratification of the Baltic Sea. A recent warming trend in sea-surface waters has been clearly demonstrated by in situ measurements, remote sensing data and numerical models. Trends in sea-surface temperature (SST) for the past three to four decades based on remote sensing data generally agree with trends determined from in situ observations. Models suggest the current warming within the Baltic Sea lies within the range experienced during the past 500 years. The salinity and stratification of the deep waters are strongly linked to the major inflows of North Sea water that occur sporadically and bring high-saline water into the deep layers of the Baltic Sea. The major inflows normally occur during winter and spring and bring cold oxygen-rich waters into the deep basins. Since 1996, large inflows have also occurred during summer, bringing in warm low-oxygen water. IntroductionChanges in thermohaline characteristics and stratification of the water column are usually analysed on the basis of data from repeat hydrographic observations, originating from shipborne monitoring programmes and/or permanent coastal and offshore oceanographic stations. Such datasets are described in recent books by Feistel et al. (2008) and Leppäranta and Myrberg (2009). In situ observations are often irregular in space and time, especially for offshore areas; therefore, trends and variability in the ocean state can only be determined by careful pre-processing of the data to address issues such as data homogenisation and the suppression of aliasing errors. In recent decades, horizontal undersampling by in situ measurements has been partially offset by the remote sensing of sea-surface properties from satellites; with these data free of spatial aliasing errors due to their high horizontal resolution. Satellite-derived cloud-free products for sea-surface temperature (SST) have been reasonably accurate since the 1980s. Many of the papers published over the past decade that address trends and variability in the circulation and stratification of the Baltic Sea are based on remote sensing data, often in combination with in situ observations and the results of numerical modelling. Improvements in the physical and numerical features of the models, accompanied by model validation studies, have increased confidence in the realism of the model results. Models provide dynamically balanced gridded datasets over decades or longer, including information for 'noisy' variables such as currents, transport and mixing fluxes. This chapter analyses the recent peer-reviewed literature, extending the findings from earlier review (Box 7.1).

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Salinity and hypoxia in the Baltic Sea since A.D. 1500

Cited by 23 publications

References 28 publications

The climate in the Baltic Sea region during the last millennium simulated with a regional climate model

The climate in the Baltic Sea region during the last millennium simulated with a regional climate model

Future changes in the Baltic Sea acid–base (pH) and oxygen balances

Recent Change—Marine Circulation and Stratification

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