Glossary

B

bacterioplankton — single-celled prokaryotes, i.e., small organisms that lack a nucleus (Bacteria and Archaea), in the water column, mainly consuming organic carbon as energy and carbon sourceon

benthic — related to the bottom of the sea including the top sediment layers

biota — plant and animal life in an area, habitat, or period

blue carbon (BC) — in marine sciences, organic carbon that is captured and stored by marine and coastal ecosystems (the abbreviation clashes with black carbon in atmospheric sciences)

blue carbon ecosystems — vegetated coastal ecosystems that capture organic carbon

biogeochemical cycle — a set of processes by which a chemical element is transformed to different chemical substances through the biotic and abiotic parts of an ecosystem

biodiversity — variety of all living things on Earth

biomass production — production of organic matter

brownification — darker water due to more organic substances and iron 

C

carbon flux — amount of carbon exchanged between carbon pools on Earth

carbon sink — accumulates carbon more than releases and thus lowers the atmospheric concentration of CO2, for example the ocean

carbon source — releases more carbon than absorbs and thus increases the atmospheric concentration of CO2, for example burning of fossil fuels

climate refuges — areas in which temperature increase is expected to be lower than on average, important areas for conservation 

climate change — climate change means a change in average or in variation of conditions in the state of the climate over a long period of time, typically decades or longer, and can be caused by natural processes or external activities, such as changes in solar cycles, volcanic eruptions and changes in atmosphere and land use caused by humans

climate change signal — observed long-term trends and projections linked to climate change

climate model — complex mathematical representation of the climate system, used to project future climate conditions and to understand past climates

climate projection — simulation of Earth’s climate far into the future, derived using climate models and assumptions of future developments of climate drivers (e.g., greenhouse gases, land use)

CO2 species — composed of chemically identical molecular entities with CO2, i.e., CO2, H2CO3, HCO3^– and CO32^–

cyanobacterial blooms — blooms in the water formed by microscopic single-celled cyanobacteria (aka blue green algae), common in the Baltic Sea during summer due to high level of eutrophication and warm water

D

DIN — dissolved inorganic nitrogen 

DIP — dissolved inorganic phosphorus

demersal — area near the sea bottom, for example demersal fish live on or near the sea bottom 

deoxygenation — the removal of oxygen atoms from an environment, substance, or molecule, i.e., decline of oxygen, the primary cause of deoxygenation in the Baltic Sea is eutrophication, deoxygenation leads to hypoxia with detrimental effects on biota 

E

ecosystem function — physical, chemical, and biological processes that transform energy, nutrients, and organic matter in an ecosystem; capacity of an ecosystem to provide goods and services that are potentially useful to humans

ecosystem functioning — interaction between an ecosystem and its environment, for example biotic activities affect the physical and chemical conditions of their environment

ecosystem services — services and benefits to humans provided by the nature and healthy ecosystems, commonly assessed as supply (mostly related to the biophysical or ecological characteristics of the environment), demand (mostly societal drivers) and flow (actual provision and use)

erosion — geological process by which surface material (e.g., soil, rock) is worn and transported, caused by natural processes such as wind, water, and ice 

estuary — partially enclosed coastal area extensively influenced by river freshwater discharge causing brackish water conditions and estuarine circulation 

euphotic zone, photic zone — water layer close to the surface with sufficient amount of light for photosynthesis (i.e., transfer of CO2, water, and sun light into chemical energy mainly by plants and zooplankton)

eutrophication — excessive growth of phytoplankton, algae, and plants, caused by excessive input of nutrients to the marine environment; excessive eutrophication causes reduced light conditions, oxygen depletion, cyanobacterial blooms, and other ecosystem changes 

euxinia — anoxia with raised level of free hydrogen sulfide (H2S) in the water

evolution — the development of new species by mutation of the genome and natural selection

exoskeleton — external skeleton that protects an organism; acidification may impair marine organisms, such as mussels, that build their exoskeleton out of calcium carbonate

extractive farming — aquaculture where for example blue mussels and macro-algae are harvested as a way to recover excessive marine nutrients for terrestrial use

F

fetch — the distance over which wind blows

foodweb — representation of who eats what in an ecosystem, describes the movement of energy and nutrients through an ecosystem, contains different trophic levels 

G

genetic diversity — variation in the genetic composition among individuals, species or a community, genetic diversity is important for adaption to changing circumstances and is an important part of biodiversity 

greenhouse gases (GHGs) — gases that absorb heat in the atmosphere, the main greenhouse gases are water vapor, carbon dioxide (C02), methane (cH4), Nitrous oxide (N20), fluorinated gases and ozone 

H

haline — saline, salty

halocline — vertical zone in the water column in which salinity changes rapidly, usually causing strong stratification of the water due to resulting different densities with higher densities for higher salinities, permanently found in large parts of the Baltic Sea and located below the mixed surface water layer

haul-out — land area for resting, breeding, foraging etc. of a seal or other marine mammal

hypoxia — low oxygen level in the environment or tissues of a body of an organism 

I

instrumental period — time period of 1886–2017, routine weather observations at fixed sites started in the beginning of the instrumental period

K

keystone species — organism that has a substantially large effect on the communities in which it occurs, helps to maintain local biodiversity, for example bladder wrack (Fucus vesiculosus) in the Baltic Sea

M

macrophyte — large aquatic plant

meteotsunami — sea level extreme travelling in phase with atmospheric low-pressure systems

mixed layer — the surface water layer, which is well mixed, oxygenated, and of uniform density 

Major Baltic Inflows (MBIs) — large, meteorologically driven saltwater inflows to the Baltic Sea which sporadically renew the deep water with saline, oxygen rich water; this is the only process that effectively ventilates the deep water of the Baltic Sea.

N

nature-based solutions (NBSs) — actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits (IUCN description)

non-indigenous species (NIS) — species not native to the geographic region of interest, but transferred there by human activities

North Atlantic Oscillation (NAO) — describes the intensity of the westerly flow. A positive NAO is related to mild, wet winters and increased storminess over northern Europe

nucleus — a separate entity in a cell surrounded by a membrane where the genome is situated, is characteristic of plant and animal cells

O

ocean acidification — decrease of seawater pH, due mostly to the rising CO2 concentration in the atmosphere and its exchange with the surface seawater

open-cage farm — aquaculture in open-top cages in coastal waters or lakes

organic matter — carbon-based compounds found in nature, e.g., in plants, animals, their remains and dissolved organic matter in the water

P

pCO2 — partial pressure of CO2

pH — measure of acidity or basicity of a solution, acidic solutions (values <7) have lower pH values than basic or alkaline solutions

paleoclimate period — time period before 1886 from which no instrumental climate records are available

pelagic — refers to the water column above the bottom and below the sea surface in open sea regions

phenological mismatches — a mismatch in the timing of the life cycle between different organisms and environmental features, for example hatching of juveniles during sub-optimal conditions

phenology — the study of cyclic and seasonal natural phenomena, especially in relation to climate and plant and animal life

phenotypic or behavioural spawning 

characteristics — changes in behavior or appearance related to spawning, e.g., muscle tissue of fish becoming lighter and of inferior quality for food consumption during spawning

photosynthesis — conversion of sun light energy to chemical energy by plants, algae, and certain bacteria, binds carbon dioxide and produces oxygen, crucial for maintenance of life on Earth

phytoplankton — photosynthesizing microscopic marine organisms, inhabit the upper water layer, foundation of the aquatic food web

piscivorous fish species — fish that eat other fish

primary production — synthesis of organic compounds from carbon dioxide by plants and other organisms capable of photosynthesis. Oxygen is an important by-product of photosynthesis.

protozoa — unicellular organisms of many species eating other small organisms or bacteria

pycnocline — vertical zone in the water column in which density changes rapidly caused by corresponding changes of temperature and/or salinity with lower densities to the surface and higher densities to the bottom due to stratification

R

radiative forcing — difference between solar energy absorbed by the Earth and radiated back to space

range shifts — changes in the distribution limits of a species

refractory compounds — chemical compounds difficult to decompose and use as food

regime shifts — large, persistent change in the structure and function of an ecosystem, e.g., in Central Baltic Sea a previously cod-dominated system changed to domination by small pelagic fish, due to overfishing, eutrophication and climate change

remineralization — breakdown or transformation of organic matter to inorganic chemical compounds

Representative Concentration Pathway (RCP) — used to describe different climate futures depending on the greenhouse gas (GHG) emissions in the coming years. The RCPs indicate a possible range of radiative forcing in the year 2100 compared to 1850.; the RCPs include a “mitigation” scenario which aims to keep global warming below 2°C above pre-industrial temperatures (RCP2.6) and a high emissions “worst case” scenario (RCP8.5) that corresponds to a future without climate mitigation; One intermediate scenario is the RCP4.5 which likely results in global mean temperature rise between 2–3°C degrees by 2100.

recruitment — successful reproduction and survival of offspring

run-off — waterflow on land when the amount of water exceeds the ability of land to absorb water, increased river run-off increases input of nutrients to the Baltic Sea

climate scenario — representation of future climate

S

scenario simulations — simulations of future climate using numerical climate models driven by different assumptions on the future development of greenhouse gas emissions, land use, and aerosol emissions 

sediment budget — balance between sediment added and removed from a coastal system

stratification — vertical ordering of inhomogeneous sea water according to its different densities due to gravitation, different densities in sea water are caused by temperature and/or salinity variationsthermocline — vertical zone in the water column in which temperature changes rapidly usually causing stratification of the water due to resulting different densities with lower densities for higher temperatures, in most parts of the Baltic Sea seasonally found with heated surface water in summer

T

thermodynamic equilibrium — the state of a system which is reached when it does not change by itself anymore, i.e. the (macroscopic) thermodynamic variables describing the system, the so-called state variables, remain unchanged over time; a set of state variables fully describing a system of sea water is, for example, salinity, temperature and pressure.

trophic cascade —  a change of one species or trophic level of the food web (such as removal or addition of top predators) that triggers substantial changes in ecosystem structure, nutrient flows, and ecosystem functions

trophic level — a group of organisms in a food web of similar size

Z

zooplankton — microscopic marine organisms which are not photosynthesizing, but feed on other organismsk (Fucus vesiculosus) in the Baltic Sea