Ocean VL 3

Question 1

What are the main geographic and hydrological features of the Baltic Sea?

Answer 1

• Type: Intra-continental marginal sea with a narrow connection to the North Sea.
• Area: 412,560 km² (including the Kattegat).
• Volume: 21,631 km³.
• Depth: Maximum depth is 459 m (Landsort-Tief), with a mean depth of 55 m.
• Salinity: Brackish water with a mix of freshwater and saltwater.
• Tides: Practically no tides (5-10 cm variation).
• Freshwater Input: Significant inflow from rivers (420-550 km³ per year).

Question 2

How has the Baltic Sea’s salinity and water levels changed over time?

Answer 2

Ancylus Lake (8,800 years ago): A freshwater lake with a sea level 30 m lower than today.

Littorina Sea (6,000 years ago): More saline than today due to higher seawater inflows.

• The current brackish state is a mix of river water and seawater, with four parts freshwater to one part seawater

Question 3

What are the carbon fluxes in different regions of the Baltic Sea, and what is bacterial growth efficiency?

Answer 3

Bothnian Bay:
* Primary production (PP) = 24 mmol C dm²/year,
* Bacterial production = 17 mmol C dm²/year (75% of PP),
* Allochthonous input = 18 mmol C dm²/year.

Bothnian Sea:
* PP = 91 mmol C dm²/year,
* Bacterial production = 34 mmol C dm²/year (37% of PP),
* Allochthonous input = 8 mmol C dm²/year.

Bacterial Growth Efficiency: 30% (bacteria convert 30% of organic carbon into biomass).

Question 4

What are the major anthropogenic pressures affecting the Baltic Sea?

Answer 4

• Pollution: Inflow of pesticides such as dioxins.
• Nutrient Inflow: Excess nitrogen and phosphorus from agriculture, causing eutrophication.
• Overfishing: Depletion of fish stocks.
• Shipping: Increased maritime traffic contributes to pollution and non-indigenous species introduction.

Question 5

What are the consequences of eutrophication in the Baltic Sea?

Answer 5

1. Nutrient Overload: Leads to excessive algae growth, particularly cyanobacteria blooms.
2. Oxygen Depletion: As algae decompose, oxygen in the bottom waters is consumed, leading to hypoxic zones (dead zones).
3. Hypoxic Zone Expansion:The hypoxic zone has increased tenfold over the past 115 years, severely affecting benthic and pelagic ecosystems.

Question 6

How are warming and ocean acidification affecting the Baltic Sea?

Answer 6

Warming:
* The Baltic Sea has warmed by 1.5°C over the past 30 years,
* especially during spring and winter, making coastal systems more vulnerable to nutrient loading.

Acidification:
* High partial pressure of CO₂ (PCO₂) in surface waters, combined with low oxygen,
* increases stress on marine organisms and amplifies acidification effects.

Question 7

What are the key governance bodies and policies for managing the Baltic Sea?

Answer 7

1) HELCOM (Helsinki Commission, 1974): First regional sea convention aimed at protecting the marine environment, targeting sources of pollution and eutrophication.

2) Baltic Sea Action Plan (BSAP, 2007): Established nutrient reduction targets for nitrogen and phosphorus.

3) EU Directives: The Urban Waste Water Treatment Directive, Nitrate Directive, and National Emission Ceilings Directive all contribute to nutrient management.

Question 8

What are the successes and challenges in managing the Baltic Sea?

Answer 8

Successes: Reduction in nutrient inputs from 1985-1995, with nitrogen reduced by 50% and phosphorus by 70%
.
Challenges: Current nutrient loads need to be reduced by a further 13% for nitrogen and 41% for phosphorus to fully meet BSAP targets.
Ongoing eutrophication and hypoxic zones remain significant issues.