Fjord systems and archives: a glossary of common terms

W.E.N. AUSTIN

School of Geography & Geosciences, University of St Andrews, St Andrews, Fife, Scotland, KY16 9AL, UK (e-mail: bill.austin@st-andrews.ac.uk)

The following glossary has been compiled and edited by William Austin (WA), with contributions from a selection of authors of the current volume: Finlo Cottier (FC), Matthias Forwick (MF), John Howe (JH), Kate McIntyre (KMc), Martyn Stoker (MS) and Matthias Paetzel (MP). This glossary is intended to provide a useful listing of the most common technical terms encountered in the current volume. The definitions employed are purposefully brief, use plain language where possible and are intended as non-technical explanations.

Anoxic: In the absence of oxygen.

Atlantic Water (AW):  Warm and saline water mass that originates in the Gulf Stream and is carried northwards in the North Atlantic Current.  Atlantic Water is a major source of heat into the Arctic where it enters through the Fram Strait and the Barents Sea.  Atlantic Water also recirculates south through the Greenland Sea. (FC)

Bioturbation: The mixing of sediment due to organism activity. Bioturbation often indicates the availability of free oxygen in the bottom waters. Anoxia would lead to the formation of laminated sediment instead. (MP)

Bottom Water: A general term for water which occupies the deepest part of the water column. (FC)
	
Brackish: Water of reduced salinity owing to mixing of seawater with freshwater. (KMc)

Brine: Seawater having enhanced salinity and therefore high density, formed in polar regions during the growth of sea ice where it is retained within the ice or released into the underlying water. (FC)

Broad Fjord: A fjord where the width of the fjord is greater than the local Rossby radius of deformation so that rotation becomes an important part of the dynamics. (FC)

Buoyancy: A force generated by differences in density (generated by changes in the temperature or salinity of the water) generally causing water to rise or sink relative to its surroundings. (FC)

Cascade: Descent of cold dense shelf waters down the continental slope often in a plume. (FC)

Convection: Movement of a fluid resulting from density instabilities. In sea water, this is usually driven by surface cooling or by increased surface salinity due to evaporation or brine rejection. (FC)

Coriolis force: The effect of the earths rotation on a fluid deflecting it to the right in the Northern hemisphere and to the left in the Southern hemisphere. 

CTD: An oceanographic sensor that measures conductivity temperature and pressure (the “D” stands for the implicit conversion to depth). From these three parameters the salinity and density of the water can be calculated. (FC)

Creep: The slow down slope movement of sediment due to gravity. (JH)
 
Debris Flow Deposit: Sediment deposited by mass failure that is commonly a  poorly sorted, matrix-supported admixture of gravel, sand and mud, which is internally disorganised. (MS) 

Debris Lobe: Lobate morphology (especially observed on seismic profiles and swath bathymetry) of debris flow deposits. (MS)

Deep Water Renewal Event: Dense water flows over a sill into the interior of a fjord basin. (WA)

Delta: Onshore and submarine deposit supplied as bedload from a river or glacier. (JH)

Diamicton: Non-sorted deposit containing a wide range of particles. (MF)

Drumlin: Elongated elevation commonly parallel to ice flow, usually comprising glacial debris. (MF)

Diatom: Siliceous microscopic autotrophic algae.(JH)

Dinoflagellate Cyst: The resting stage of a group of motile, planktonic micro-organisms, typically composed of a complex organic polymer called dinosporin and found in both marine and freshwater environments. (JH)

Epifauna: An organism which lives on or above the sediment (or any other substrate) surface. (WA)

Englacial: sediment derived from within a glacier. (JH)

Erratic: A boulder of typically non-local origin transported by ice. (KMc)

Esker: Irregular ridge of sand and gravel deposited from meltwater streams within a subglacial, englacial or supraglacial drainage network. (MF)

Estuarine circulation: Density driven water circulation in fjords resulting from the combination of outward flowing brackish surface waters and inward flowing saline deeper waters, often across sills. This process usually leads to oxygen renewal across at least parts of the fjord water column. (MP)

Fan: Lobate deposit of fine-grained sediments deposited from suspension from a river or glacier. (KMc)	

Fast ice: Sea ice that remains fast along the coast, over shoals, or between grounded icebergs (also called landfast ice). (FC)

First-year ice: Ice with no more than one year’s growth. Level when undeformed, but where ridges and hummocks occurs, it is rough and sharply angular. (FC)

Foraminifera: Single-celled protista some species of which produce calcium carbonate tests used as a water mass proxy for palaeoceanographic reconstructions. (KMc)

Fjord: A long, narrow inlet with steep sides formed within a glacially-eroded valley. (WA)

Glacier surge: A relatively short period (some years) of rapid glacier advance resulting from oscillations in the internal glacier configuration and enhanced basal sliding. (MF)

Glacimarine: Environments that are influenced by tidewater glaciers and/or sea ice. (MF)

Halocline: An increase in sea-water salinity over a short depth change. It typically marks the lower boundary of the mixed layer and is usually coincident with the pycnocline in polar waters. (FC)

Heat Flux: The rate at which heat is transported through, or by, a material, e.g. water, air and ice; defined as the flow of energy per unit area per unit time. (FC)

Ice rafted detritus (IRD): Material that is transported by (i.e. ice rafted) and deposited from icebergs and/or sea ice. (MF)

Ice stream: A fast flowing stream of ice within an ice sheet. (KMc)

Infauna: An organism which lives within the sediment (or any other substrate). (WA)

Isostatic readjustment: Crustal unloading due to disappearance of a continental ice-sheet. The loss of the weight of the ice causes the underlying crust to uplift from its previous depressed state. This has the effect of lowering regional sea level, as the continent rises. (JH)

Katabatic: A strong wind which carries dense cold air down a slope under gravity. In the polar regions they are often in an offshore direction. The cold air and strong winds promote sea ice growth. (FC)

Lamination: Millimeter scale thin bands of sediment occurring in seasonal succession mostly forming during conditions of oxygen depletion or anoxia. See also “seasonal lamination” and “varves”. (MP)

Maerl: Calcareous gravels formed by the accumulation of slow-growing unattached nongeniculate Corallinaceae (Rhodophyta), commonly known as calcareous red seaweed. (WA)

Mass Failure: Gravity-driven downslope motion of rock and regolith. (MS)

Mass Flow: Downslope mass movement of rock and regolith in which shear stress is disturbed throughout the mass (MS).

Macrofauna: Benthic fauna more than 1mm in size. (JH)

Meiofauna: Benthic fauna between 0.5mm-0.62 microns in size. (JH)

Microfauna: Benthic fauna below 0.1mm in size. (JH)

Mineral matter: All solids originating from rock erosion. In fjords they consist of the grain sizes clay (<2μm), silt (2-63μm) and sand (63μm-2mm). Occasionally also larger particles might occur in terms of drop stones or from slides. (MP)

Mini-ocean: Fjords are representing marine realms. Depositional and oceanographic processes are similar to those of the oceans. The advantage of fjords is that the study of these marine processes is confined to limited areas and can be studied at very high resolution. Thus, fjords can be treated as mini-oceans and findings might be transferred into larger ocean models. (MP)  

Moraine: Ridges or mounds deposited by a glacier. (MF)

Mud: Organic matter rich silty clay. (MP)

Multibeam bathymetric sonar: An elaborate sonar used to accurately measure the shape of the seafloor. These systems use multiple beams of sound, a number of times a second in a fan or cone or sound (sometimes termed ‘swath’) either side of the vessel. (JH)

Neotectonics: Most recent tectonism and its effects. (MS)

North Atlantic Oscillation (NAO): A climatic phenomenon in the North Atlantic Ocean region, indexed by the difference in atmospheric pressure at sea level between the Icelandic low and Azores high. (WA)

Nutrient supply: Nutrients are chemical substances to nourish organisms, occurring as e.g. nitrogen, phosphate or carbon compounds, or in ionic form as e.g. silica or iron. Nutrients are supplied to fjords through either rock and soil weathering and dissolution from land, or they enter the fjord from the sea during circulation and deep water renewal processes. (MP)

Organic matter: organic matter in fjords and fjord sediments consists of a combination of terrestrial organic matter originating from higher land plants, and marine organic matter derived from primary production of the fjord photic zone. In some exposed fjords, also sewage might contribute a part of the fjord organic matter composition. (MP)

Oxygen depletion: The process of using up free oxygen during organic matter decomposition within a fjord basin. (MP)

Oxygen renewal: The process of adding oxygen to the fjord basin water column mostly due to enhanced estuarine circulation or deep water renewal. (MP)

Palynology: Study of organic-walled microfossils such as pollen and dinoflagellates.

Paraglacial: Non-glacial processes, sedimentation and landscape development directly conditioned by glaciation and deglaciation. (MS)

Pockmarks: Shallow, small, generally circular depressions on the seafloor usually formed where gas or other fluids are expelled from the underlying sediments (MS).

Polar Surface Water (PSW): The general term given to the rather fresh water mass which occupies the mixed layer of the Arctic Ocean. (FC)

Polynya:   Non-linear opening enclosed by ice that may be formed as a latent heat  polynya, formed near coastal areas or islands by wind displacement (or coastal), or a sensible heat  polynya formed by the upwelling of warm water (or deep ocean). (FC)

Primary Productivity: Rate of biomass production through chemosynthesis or more commonly photosynthesis. (KMc) 

Proxies (or proxy variables): Often biogenic components, having a close relationship to environmental parameters and providing measurable descriptors of key climatic and environmental variables. (WA)

Pycnocline: An increase in sea-water density over a short depth change. It usually marks the lower boundary of the mixed layer. (FC)

Redox Boundary: Reduction, oxidation. The level within the sediment below the seafloor where oxygen is sufficiently depleted to inhibit aerobic respiration. (KMc)

Regression: Fall in sea level. (JH)

Respiration: The rate of biomass, i.e. organic matter decomposition using free oxygen, occurring either in the water column or in the sediment. (MP)

Rossby radius of deformation: A length scale at which it becomes important to consider the rotation of the ocean in relation to flow.  It is typically in the kilometre range and tends to be smaller in the polar regions because it is related to latitude. (FC)

Runoff: Water flow from land resulting either directly from precipitation or from river flow. Runoff can be seasonally enhanced during melt water supply. Runoff provides an effective way of transporting terrestrial material into the fjord. (MP)  

Scarp (abbreviation of escarpment): Steep slope or cliff found at margin of a flat or gently sloping surface (MS).

SCUBA: An acronym for Self Contained Underwater Breathing Apparatus. (WA)

Seasonal lamination: All seasonal change or events (blooms, precipitation, storms etc.) leave traces in the sediment. Anoxic conditions might preserve these traces to form lamination. The succession of lamination represents the number of annually occurring seasonal events, often not only restricted to the varve doublet of summer and winter deposition. (MP)

Sediment trap: A device placed on or above the sea floor to collect particulate matter settling through the water column. Fjord basins are often referred to as natural sediment traps. (JH & MP)

Seiche: An internal oscillation in a fjord due to the formation of a standing wave within the body of water. (FC)

Sensible heat:  Potential energy in the form of thermal energy or heat. (FC)

Sill: A topographic shallowing of the fjord seafloor. Either bedrock or morainic in composition. Typically occurring at the fjord mouth. (KMc)

Slartibartfast: A fictional character created by Douglas Adams in his book The Hitchhiker’s Guide to the Galaxy. A Magrathean and a designer of planets, he won a design award for the fjords of Norway on planet Earth. (WA)

Slide: Downslope mass movement of essentially rigid, internally undeformed masses of rock and regolith along discrete shear surfaces, which are commonly either planar (translational) or curved (rotational) in form.  (MS)

Slump: Rotational slide or curved surface. (MS)

Stadial: A millennial-scale cold episode characterizing periods of deglaciation e.g. Younger Dryas Stadial (13-11.5 ky) (KMc)

Stratification: Separation of the water column into layers based on density. (KMc)

Subglacial: Sediment derived from below a glacier. (JH)

Suess effect: Anthropogenic enrichment of carbon-13 in the atmosphere and ocean resulting from the burning of fossil fuels. (KMc)

Syn-sedimentary fault: A fault in the sediment overburden produced by the weight of sediment, occurring shortly after or during deposition. (JH)

Tidewater glacier: Non-floating glacier margin where the ice terminates at a cliff at the grounding line of the glacier. (MF)

Till: Poor- to well-sorted sediment with a wide variety of grain sizes deposited directly from a glacier. (MF)

Transgression: A rise in sea level. (JH)

Tsunami: A series of water waves caused by the displacement of a large volume of water. (WA)

Turbidity Current: Episodic currents of sediment-laden water that sweep across the seafloor. (MS)

Turbulence: Small scale motions in sea water that causes heat, salt and dissolved components to be mixed or dispersed through the water. (FC)

Two-Way-Time: The time taken for a pulse of sound to travel through the water column and the sub-seabed and back to the surface. Used when calculating sediment thicknesses from seismic reflection profiles. (KMc)

Varves: Glacially derived sedimentation of lamination doublets (mm- to cm-scale) resulting from rhythmic strong summer melting and low winter activity. (MP)