Course:EOSC270/2023/Group 6 - The Impacts of Salinity Change on Marine Ecosystems

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Background Information about Salinity? (Danny)

Background

Global annual mean sea surface salinity from the World Ocean Atlas 2001

Salinity is a vital parameter for determining the state of the ocean and plays a critical role in understanding the ecological environment and ocean circulation[1]. Generally, ocean salinity has increased in some regions, particularly in the subtropics over several decades, and decreased in others, especially in the high-latitude oceans[2].

Salinity Measurement

Two typical methods used to measure salinity include a conductivity sensor and satellite measurements. The conductivity sensor is placed on the back of a fish, exposed directly to seawater, and measures temperature, pressure, light intensity, and electrical conductivity to calculate salinity using an equation[3].

Satellite measurements can also determine salinity levels in two ways. The first involves correlating satellite measurements of radiosity or reflectivity to salinity. The second is the detection of colored dissolved organic matter (CDOM) using Marine color satellite products, suitable for use close to the shore, which effectively calculates the actual salinity[4].

Salinity and The Marine Cycle

Ocean surface salinity is a critical factor in understanding how freshwater input and output impacts ocean dynamics, as the majority of global evaporation (86%) and precipitation (78%) occur over the ocean [5]. Notably, there is a vast expanse of highly saline water in the North Atlantic, similar to terrestrial deserts that experience minimal rainfall and significant evaporation[5].

Monitoring changes in ocean surface salinity allows us to keep track of fluctuations in the water cycle, as salinity variations very sensitively reflect the overall exchange of freshwater between the ocean and the atmosphere. The process of evaporation transfers freshwater from the ocean into the atmosphere, thereby increasing the ocean's salinity. Conversely, precipitation adds freshwater to the ocean, leading to a reduction in its salinity. Therefore, changes in salinity provide an excellent indication of changes in the water cycle, encompassing the impact of various factors over vast areas[6].

Averages sea surface temperature for the El Nino in December 1982 and June 1983.

Salinity Problems

In the late 20th century, salinity levels decreased in the continental margin of Antarctica and the Pacific Ocean[7]. The El Nino Southern Oscillation (ENSO) is an oscillation of wind field and sea surface temperature in the eastern equatorial Pacific that can affect and alter atmospheric circulation, resulting in global environmental impacts, despite originating in the tropical Pacific Ocean[8]. La Nina events refer to a widespread and persistent abnormal cooling of sea surface temperatures in the eastern and central equatorial Pacific Ocean, also known as an anti-El Nino. Salinity plays a positive role in the emergence of El Niño by increasing the variation in density, which is more negative during El Nino and more positive during La Nina[9].


How does this problem impact marine ecosystems?

Changes in salt concentration will have a variety of effects on the world and marine life, including climate warming and a decrease in the area of the world's sea ice, which will alter the habitat of marine life. Changes in salt concentration will also cause changes in the organism traits of marine animals and plants.

The pacific ocean salinity decrase(Jeffrey)

Human activities impact the marine ecosystem, affecting temperature, acidification, and salinity[10]. There are three major types of salinity processes: pure warming, pure freshening, and pure heave[11]. . The north Pacific Ocean experiences pure freshening due to increased freshwater flux from nearby rivers[11]. The freshening of the Pacific Ocean can cause instability in the salinity level, which may lead to diseases in the ocean ecosystem[12].

Steady state surface temperature differences for 50 g/kg versus 20 g/kg salinity scenarios with each model configuration. Reds indicate higher temperatures with higher salinity while blues indicate lower temperatures with higher salinity. All high salinity scenarios are warmer on global average than the low salinity scenarios despite local cooling.
Steady state surface temperature differences for 50 g/kg versus 20 g/kg salinity scenarios with each model configuration.

Changes in habitants

Sea ice coverage for various model configurations and ocean salinities. Rows show the standard model with a fully coupled ocean-atmosphere, sea ice dynamics, and freezing point depression (“Full Physics”; top); a modified model configuration with ocean and sea ice dynamics but fixed freezing point for all salinities (“Fixed Freezing Point”; middle); and a slab ocean configuration lacking ocean and ice dynamics but including freezing point depression (“No dynamics”; bottom). Salinity differs between the columns, increasing from 20 (left) to 50 g/kg (right). Increasing salinity yields lower ice cover in all scenarios, but the effects are most pronounced in model scenarios that include both dynamical and thermodynamic effects.
Sea ice coverage for various model configurations and ocean salinities.

Increasing ocean salinity results in warming, particularly at high latitudes. With Fixed Freezing Point, increasing salinity from 20 to 50 g/kg results in warming of up to 11.3°C in the annual average at northern high latitudes (0.8°C warming on global average) and a 71% decrease in global sea ice coverage[13]. Global sea ice loss and melting will alter the habitats of marine animals and plants, especially those that depend on sea ice for mating, raising their young, and resting, such as seals, walruses, penguins, etc. Loss of habitat would result in a decline in the numbers of these marine mammals, as well as the marine species that depend on them.

Changes in organism traits

Salinity variations  can affect organism characteristics such as survival, fecundity, metabolic rate, and growth rate. For example, Garreta-Lara et al. [14] found a strong influence of salinity on the metabolomic profile of the invertebrate Daphnia magna, but no significant interaction with temperature. In estuarine and marine invertebrates, increased salinity generally protects against the negative effects of metals [15], which can be partly explained by competitive interactions with major cations for sensitive ion transport sites [16].

Example of changes in salinity affecting the Pacific

Salinity has an impact on the size of eggs in Pacific herring. By setting and controlling variables experimentally, it is observed that there was an inverse relation, between egg volume and salinity at all stages of egg development. Eggs transferred from 20‰ to 5 or 35‰ S, 87.4 hr after fertilization (90% blastodermal overgrowth of the yolk), showed only minor changes in total egg volume within the period of relative stability (100–240 hr)[17].

Oysters and other Pacific invertebrates rely heavily on their habitat for growth. In high growth sites, oysters had greatest increases in shell height and weights of whole oyster, shell and dry meat which were attributed to high phytoplankton biomass (chlorophyll a) and suitable temperature and salinity regimes[18]. Oyster quality and production fall when the salinity of the Pacific Ocean varies due to the decline in phytoplankton population and the shift in salt concentration.

The extent of the problem and future trend

Current situation of the Pacific Ocean

In summary, the present ocean salinity situation is very complex and influenced by a combination of IPO, global warming and salinity advection.

IPO

Two phases of IPO
SPCZ AND ITCZ

IPO is a large-scale, long-term oscillation affecting the climate of the Pacific basin. During the positive phase of the IPO, precipitation in the northeastern South Pacific Convergence Zone (SPCZ) is generally higher, while precipitation in the southwestern SPCZ is generally lower[19]. For the Pacific Ocean, decadal salinity changes are closely related to the decadal Pacific Oscillation (IPO)[20]. A salinity pattern is followed: salinity is low where precipitation is high and high where precipitation is low[20].

Global warming

Notably, previously mentioned salinity pattern is now reinforced by the effects of anthropogenic global warming, implying that the ocean becomes fresher in precipitation-dominated areas and more saline in evaporation-dominated areas[21]. Argo data shows that the contrast between low and high salinity is increasing in all regions except the subpolar North Atlantic[22].

Salinity advection

The salinity advection is mainly driven by winds, where seawater with high salinity in the subtropics is carried to the tropics, while fresher water in the tropics is transported to higher latitudes[21]. In summary, salinity advection contributes negatively to salinity variability in the ITCZ and SPCZ regions, positively to the equatorial central Pacific, and smooths the salinity gradient[23].

different level of salinity and affect to shell species

Salinity drop and costal ecosystem species

The salinity decrease is now influencing the coastal species. Scientists found some species with hard shell in the costal low salinity environment has higher chance to loose their shell than open ocean high salinity environment[10]. Due to the increasing amount of freshwater being added to the ocean, the salinity levels near the coast are decreasing. This is causing living environment of shell species closer to the coast is fresher than before[10].


What may happen if Salinity increasing in future

On the other aspact, The increasing ocean salinity level may cause some diseases in the ocean ecosystem in the future. A study of a disease shows that a kind of sea grass called eelgrass has a lower chance to be infected by disease in the high temperature and low salinity environment[24]. This disease was appear in 1903s in Altlantic ocean, that was cause a large area infected of the sea grass[24]. If human not control the waste water gose into the ocean, in the future the salinity may increase, and it will lead to the disease outbreaks like the seagrass in the Altlantic ocean.

disease possibility in different salinity level


The future if human do not act

A recent study suggests that the global ocean is a rapidly changing system that is impacted by variations in temperature and salinity[25]. .Salinity changes can occur not only on the top layer of the ocean but also in deeper parts of the ocean, and the rate of change may increase in the future[25].The study suggests that the majority of observed changes in ocean water patterns are the result of human activity and that these changes will worsen if humans continue to emit high levels of carbon dioxide(CO2)[25]. In the future decades, if humans still do not control greenhouse gas emissions, and slow down global warming, the influence of ocean salinity change will become more visible to humans. . The study predicts that human-related influence on deep ocean basins in the Pacific Ocean will increase from 40-65% in 2050 to 55-80% in 2080[25]. This means that in the future, more and more water areas will be impacted by human activity if we continue to ignore these issues.


Given the impact, what are the solutions?

Climate Change

Principles of three main CO2 capture options.

Changing precipitation patterns and increased evaporation due to global warming could also play a role in exacerbating ocean salinity.[26] To address this issue, several mitigation strategies can be employed, such as reducing greenhouse gas emissions through the adoption of renewable energy sources, improving energy efficiency, and implementing more efficient carbon capture and storage technologies (Carbon capture and storage is the technological process of collecting carbon dioxide at sources that produce it, such as industrial facilities, and then storing them in locations that are isolated from the air).[27]

Increase River Input

Map of South-to-North Water Transfer Project

As population and industrial facilities continue to grow, the demand for freshwater resources increases, leading to a decrease in the flow of rivers entering the sea and a concomitant increase in ocean salinity.[28]Inter-basin water transfer (IBWT) is a method of reallocating water resources across geopolitical boundaries, meaning the construction of diversion projects between different basins to regulate the water balance in each basin.[29] For example, China has implemented the South-North Water Transfer Project. The South-to-North Water Transfer Project brings water from the precipitation-rich southern regions of China to the northern regions through man-made canals.[29] This reduces the northern demand for freshwater resources from rivers such as the Yellow River, increases the amount of freshwater flowing into the Bohai Sea, and regulates the salinity of Bohai Sea water.

Proper Treatment of Brine

The brine discharged from desalination is closely related to the uneven distribution of seawater salinity.[30] Measures such as locating desalination facilities in areas with ocean currents and building longer outlets can mitigate these adverse effects.[31] Studies of salinity dispersion models in Bohai Bay (an area with limited seawater exchange capacity) suggest that desalination plants should discharge their concentrated seawater at high tide and maintain a capacity of less than 10x10^4 t/d.[32] Therefore, for the ocean salinity problem caused by desalination, a rational planning of the siting and discharge pattern is essential to reduce the salinity variability.

Monitoring Salinity Change

Ocean salinity is monitored by means such as conductivity sensors and satellite technology. In order to effectively study changes in ocean salinity and develop countermeasures, ocean observing systems that can detect and monitor continuous changes must be relentlessly maintained and enhanced.[33]

References

  1. ↑ Fedorov, A; Pacanowski, S (2004). "The Effect of Salinity on the Wind-Driven Circulation and the Thermal Structure of the Upper Ocean". Journal of Physical Oceanography. 34: 1949–1966.
  2. ↑ Durack, P; Wijffels, S (2010). "Fifty-year trends in global ocean salinities and their relationship to broad-scale warming". Journal of Climate. 23(16): 4342–4362.
  3. ↑ Lewis, E (January 1980). [10.1109/JOE.1980.1145448 "The practical salinity scale 1978 and its antecedents"] Check |url= value (help). IEEE Journal of Oceanic Engineering. 5: 3–8.
  4. ↑ Merv, F (2019). "Remote Sensing for Marine Management". World Seas: an Environmental Evaluation (Second Edition).
  5. ↑ 5.0 5.1 NASA (February 23, 2023). "Salinity".
  6. ↑ "Ocean salinity: Climate change is also changing the water cycle". February 23, 2023.
  7. ↑ Stanley, J (1998). "Interannual ocean and sea ice variability in the Ross Sea". Ocean, Ice, and Atmosphere: Interactions at the Antarctic Continental Margins. 75: 135–150.
  8. ↑ Kevin, T; Grant, B (1998). "Progress during TOGA in understanding and modeling global teleconnections associated with tropical sea surface temperatures". Journal of Geophysical Research: Oceans. 103: 14291–14324.
  9. ↑ Zheng, F; Zheng, R (2015). "Interannually varying salinity effects on ENSO in the tropical pacific: A diagnostic analysis from argo". Ocean Dynamics. 65(5): 691–705.
  10. ↑ 10.0 10.1 10.2 Laurie, M. Charrieau; Helena, L. Filipsson (2018). "Decalcification and survival of benthic foraminifera under the combined impacts of varying pH and salinity". ,Marine Environmental Research. 138: 36–45. ISSN 0141-1136.
  11. ↑ 11.0 11.1 Sathyanarayanan, A.; Köhl, A.; Stammer, D. (2021). "Ocean salinity changes in the global ocean under global warming conditions. part I: Mechanisms in a strong warming scenario American Meteorological Society". Journal of climate. 34: 8219. ISSN 0894-8755.
  12. ↑ Nan, F.; Yu, F.; Xue, H.; Wang, R.; Si, G. (2015). "Ocean salinity changes in the northwest Pacific subtropical gyre: The quasi-decadal oscillation and the freshening trend". Journal of Geophysical Research: Oceans. 120: 2179–2192. ISSN 1429-2411 Check |issn= value (help).
  13. ↑ Olson, S., Jansen, M. F., Abbot, D. S., Halevy, I., & Goldblatt, C. (2022). "The effect of ocean salinity on climate and its implications for Earth's habitability". Geophysical Research Letters, 49(10).CS1 maint: multiple names: authors list (link)
  14. ↑ Garreta-Lara E, Campos B, Barata C, Lacorte S, Tauler R. 2018Combined effects of salinity, temperature and hypoxia on Daphnia magna metabolism. Sci. Total Environ. 610, 602-612. (doi:10.1016/j.scitotenv.2017.05.190) Crossref, PubMed, ISI, Google Scholar
  15. ↑ Heugens EHW, Hendriks AJ, Dekker T, Straalen NM, Admiraal W. 2001A review of the effects of multiple stressors on aquatic organisms and analysis of uncertainty factors for use in risk assessment. Crit. Rev. Toxicol. 31, 247-284. (doi:10.1080/20014091111695) Crossref, PubMed, ISI, Google Scholar
  16. ↑ Baysoy E, Atli G, Gürler CÖ, Dogan Z, Eroglu A, Kocalar K, Canli M. 2012The effects of increased freshwater salinity in the biodisponibility of metals (Cr, Pb) and effects on antioxidant systems of Oreochromis niloticus. Ecotoxicol. Environ. Saf. 84, 249-253. (doi:10.1016/j.ecoenv.2012.07.017) Crossref, PubMed, ISI, Google Scholar
  17. ↑ Alderdice, D. F., Rosenthal, H., & Velsen, F. P. (1979). "Helgoländer Wissenschaftliche Meeresuntersuchungen, 32(1-2), 163–178". Influence of salinity and cadmium on the volume of Pacific Herring Eggs.CS1 maint: multiple names: authors list (link)
  18. ↑ Brown, J. R., & Hartwick, E. B. (1988). "Influences of temperature, salinity and available food upon suspended culture of the Pacific oyster, Crassostrea gigas". Aquaculture, 70(3), 231–251.CS1 maint: multiple names: authors list (link)
  19. ↑ NIWA (July 27, 2017.). ""Interdecadal Pacific Oscillation."". Check date values in: |date= (help)
  20. ↑ 20.0 20.1 Shi, H. Y.; et al. (2022). "Salinity variability modes in the pacific ocean from the perspectives of the interdecadal pacific oscillation and global warming". Journal of Geophysical Research. Oceans. 127(7). Explicit use of et al. in: |last2= (help)
  21. ↑ 21.0 21.1 Li, G; et al. (2019). "Examining the salinity change in the upper pacific ocean during the argo period". Climate Dynamics. 53(9-10): 6055–6074. Explicit use of et al. in: |last2= (help)
  22. ↑ Hosoda, Shigeki; et al. (2009). ""Global Surface Layer Salinity Change Detected by Argo and Its Implication for Hydrological Cycle Intensification."". Journal of Oceanography 65. no. 4: 579–86. Explicit use of et al. in: |last2= (help)
  23. ↑ Qiwei, Sun; Yan, Du (2022). ""Sea Surface Salinity Changes in Response to El Niño–like SST Warming and Relevant Ocean Dynamics in the Tropical Pacific under the CMIP6 Abrupt-4xco2 Scenario."". https://doi.org/10.1175/jcli-d-21-0973.1. no. 18: 5839–54. External link in |journal= (help)
  24. ↑ 24.0 24.1 Brakel, J.; Jakobsson-Thor, S.; Bockelmann, A.; Reusch, T. B. H. (2019). "Modulation of the eelgrass – labyrinthula zosterae interaction under predicted ocean warming, salinity change and light limitation". Frontiers in Marine Science.
  25. ↑ 25.0 25.1 25.2 25.3 Yona, S.; Guilyardi, E. (2020). 10.1038/s41558-020-0878-x "Human- induced changes to the global ocean water masses and their time of emergence" Check |url= value (help). Nature Climate Change. 10(11). ISSN 1030-1036 Check |issn= value (help).
  26. ↑ Dashkevich, L. V; Berdnikov, S. V. (2016). "Climatic Changes And Salinity Of The Sea Of Azov For 100 Years". Sofia: Surveying Geology & Mining Ecology Management (SGEM).
  27. ↑ Gattuso, J.P.; Magnan, A.K. (2018). "Ocean solutions to address climate change and its effects on marine ecosystems". Frontiers in Marine Science.
  28. ↑ Fournier, S.; Lee, T. (2021). "Seasonal and interannual variability of sea surface salinity near major river mouths of the world ocean inferred from gridded satellite and in-situ salinity products". Remote Sensing (Basel, Switzerland).
  29. ↑ 29.0 29.1 Sheng, J; Tang, W (2020). "Can interbasin water transfer affect water consumption and pollution? lessons from china's South–North water transfer project". Environmental Policy and Governance. 30(6): 345–358.
  30. ↑ Fernández-Torquemada, Y.; Sánchez-Lizaso, J.L. (2005). "Preliminary results of the monitoring of the brine discharge produced by the SWRO desalination plant of alicante (SE spain)". Desalination.
  31. ↑ Purnalna, A.; Al-Barwani, H.H. (2003). "Modeling dispersion of brine waste discharges from a coastal desalination plant". Desalination.
  32. ↑ Zhang, X.; Zhang, F. (2016). "Impact prediction of the concentrated saltwater discharged from desalination plant on the distribution of the salinity in bohai bay". Hai Yang Huan Jing Ke Xue.
  33. ↑ Silvy, Y.; Guilyardi, E (2020). "Human-induced changes to the global ocean water masses and their time of emergence". Nature Climate Change.
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