Fine Temporal Scales

Transient fluctuations. The salinity of a particular location may be temporarily influenced by transient abiotic or biotic conditions. Temporary reductions in local salinity could be caused by the short-term inputs of freshwater or shading, such as during rain or flood events and additions of wrack mats, detritus, short-lived plants, or algal blooms. Salinity increases could result from removal of freshwater or structure, or addition of saline water, such as during high tide events or tidal surges that scour ground cover and increase seawater inundation, or during short periods of dry, hot temperature (Figure 4). The effects of such events may persist for a time after the actual event ends, for example, salt residue may remain in the upper intertidal following a high tide series.

Cyclic fluctuations. Frequent events such as daily and monthly tidal cycles can cause concomitant fluctuations in salinity of soils and water. Organisms within the tidal zone are either adapted to the salinity shifts or move in and out with the tides.

Seasonal fluctuation in climate and tides have similar but longer-term effects on the salinity of systems. In many arid and temperate regions, winter and early spring bring precipitation and long pulses of fresh and brackish conditions, while summer and early fall bring drier and therefore more saline conditions. Tropic regions may experience the highest salinities in the winter dry season and the lowest during summer tropical storm events. Organisms not adapted to these conditions die off or

Thermohaline circulation - The 'global conveyor belt'

Figure 3 global thermohaline circulation. Density patterns caused by differences in salinity and temperature drive global oceanic circulation patterns.

Thermohaline circulation - The 'global conveyor belt'

Figure 3 global thermohaline circulation. Density patterns caused by differences in salinity and temperature drive global oceanic circulation patterns.

Figure 4 Intertidal pools in salt marshes have salinities that are strongly affected by meteorological events (e.g., rainfall, wind), timing of inundation, and ambient air temperature. These pools can change in salinity from more than 125 psu to virtually freshwater in the course of just hours. Photo credit: D. Talley.

Figure 4 Intertidal pools in salt marshes have salinities that are strongly affected by meteorological events (e.g., rainfall, wind), timing of inundation, and ambient air temperature. These pools can change in salinity from more than 125 psu to virtually freshwater in the course of just hours. Photo credit: D. Talley.

move to more favorable environments (downstream to more saline waters if marine, or upstream to fresher conditions if not marine).

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