{"id":271112,"date":"2023-08-03T11:35:16","date_gmt":"2023-08-03T09:35:16","guid":{"rendered":"https:\/\/climatescience.press\/?p=271112"},"modified":"2023-08-03T11:35:27","modified_gmt":"2023-08-03T09:35:27","slug":"salty-news-from-an-old-salt","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=271112","title":{"rendered":"Salty News From An Old Salt"},"content":{"rendered":"\n
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From Watts Up With That?<\/a><\/p>\n\n\n\n

Guest Post by Willis Eschenbach<\/em><\/strong><\/p>\n\n\n\n

(In sailors\u2019 parlance, an \u201cold salt\u201d is some fool like myself who has spent a good chunk of their life at sea \u2026)<\/em><\/p>\n\n\n\n

It seems that climate alarmists have a new focus\u2014oceanic salinity. From the\u00a0Florida Times-Union<\/a>\u00a0I find:<\/p>\n\n\n\n

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Researchers, including in Jacksonville, warn of perilous salinity changes in warming oceans<\/em><\/strong><\/p>\n\n\n\n

Matt Soergel, Florida Times-Union<\/em><\/strong><\/p>\n\n\n\n

Fri, July 28, 2023 at 12:32 PM PDT<\/em><\/p>\n\n\n\n

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Cliff Ross, University of North Florida marine biologist and chairman of the Biology Department, explores the Dry Tortugas west of Key West. He is part of an international team of researchers who just released a paper on changing salinity levels in the ocean as an effect of rapid climate change.<\/em><\/p>\n\n\n\n

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Cliff Ross<\/em><\/a>\u00a0notes that in stories and studies on human-caused\u00a0<\/em>climate change<\/em><\/a>, most of the emphasis is on a rapidly warming world that is expected to only get hotter and hotter.<\/em><\/p>\n\n\n\n

That\u2019s fair enough, he says \u2014 and that\u2019s taken on increased urgency as intense heat waves hammer various parts of the globe this summer, a phenomenon scientists are linking to climate change.<\/em><\/p>\n\n\n\n

But Ross, a marine biologist who\u2019s head of the Biology Department at the University of North Florida and part of an international research team, wants to bring attention to another effect of a hotter Earth \u2014 changing salinity levels in the world\u2019s oceans, which could themselves bring about big changes across the planet.<\/em><\/p>\n\n\n\n

It\u2019s a complex issue, but those\u00a0<\/em><\/a>changing salinity levels could have major impacts on the world\u2019s economy, on creatures that live in the ocean and on the residents of coastal areas \u2014 Florida certainly included.<\/em><\/p>\n<\/blockquote>\n\n\n\n

So in theory, changing salinity levels \u201ccould\u201d bring about big changes, and it \u201ccould\u201d have major impacts?<\/p>\n\n\n\n

Unimpressed by the could-ness, I went to see the\u00a0underlying study<\/a>\u00a0in Global Change Biology<\/p>\n\n\n\n

It turns out that the study contains enough \u201cweasel words\u201d to equip an entire species of Mustelidae. (\u201cWeasel words\u201d are words like \u201ccould\u201d, \u201cmay\u201d, or \u201cmight\u201d that you can use so that your scientific claims can never be falsified.) Here are some examples from the study.<\/p>\n\n\n\n

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Salinity changes\u00a0may<\/strong>\u00a0impact diversity, ecosystem and habitat structure loss, and community shifts including trophic cascades<\/em><\/p>\n\n\n\n

Changes to [salinity]\u00a0may<\/strong>\u00a0strongly contribute to ocean stratification<\/em><\/p>\n\n\n\n

Reduction in [mangrove] growth \u2026 due to elevated salinity \u2026\u00a0may<\/strong>\u00a0be exacerbated by other stressors<\/em><\/p>\n\n\n\n

[Salinity] tolerant and euryhaline harmful algae blooms\u00a0may<\/strong>\u00a0be favored and impact ecosystem structure and function.<\/em><\/p>\n\n\n\n

Such species\u00a0could<\/strong>\u00a0be affected by the projected end of the century salinity changes<\/em><\/p>\n\n\n\n

Shifts in phytoplankton communities\u00a0may<\/strong>\u00a0trigger trophic cascades\u00a0<\/em><\/p>\n\n\n\n

Negative effects [of salinity] on sexual reproduction (e.g., lowered gamete viability, fertilization, and polyspermy) and altered disease susceptibility\u00a0can<\/strong>\u00a0lead to decreased genetic diversity that\u00a0may<\/strong>\u00a0change ecosystem structure and function<\/em><\/p>\n\n\n\n

Indirect effects [on seagrass] by modifying the rate of top-down interactions with grazers and metabolic disadvantages\u00a0may<\/strong>\u00a0alter ecosystem structure and function.<\/em><\/p>\n\n\n\n

Disruption of cellular processes and metabolic rates (e.g., caused by enhanced energetic requirements for osmo-adjustments) are common in marine fish and invertebrates and\u00a0may<\/strong>\u00a0disturb fertilization, development, and sensory perception<\/em><\/p>\n\n\n\n

Certain taxa, particularly those adapted to high marsh conditions,\u00a0could<\/strong>\u00a0migrate to fresher ecotones<\/em><\/p>\n\n\n\n

Although many cosmopolitan microbial taxa will persist throughout regional salinity changes, their function\u00a0may<\/strong>\u00a0change<\/em><\/p>\n\n\n\n

Sea level rise connected with salinization as well as ecotone shifts and trophic cascades\u00a0may<\/strong>\u00a0contribute to substantially altered ecosystem structure and functionality.<\/em><\/p>\n\n\n\n

It is further\u00a0predicted<\/strong>\u00a0that seawater intrusion and regional salinity increase will cause a shift from methanogenesis-dominated to sulfate reduction-dominated metabolism, which\u00a0will likely<\/strong>\u00a0lower CH4<\/sub>\u00a0production in the short term.<\/em><\/p>\n\n\n\n

Future\u00a0projections<\/strong>\u00a0from the phase 6 of the Coupled Model Intercomparison Project (CMIP6) multi-model mean \u2026 show strong salinity changes that resemble the pattern of observed changes will continue<\/em><\/p>\n\n\n\n

Mesopelagic fish larvae are usually distributed in high salinity waters, and even subtle drops in salinity (~1 psu)\u00a0may<\/strong>\u00a0impact egg and larval survival<\/em><\/p>\n\n\n\n

Salinity-enhanced stratification\u00a0may<\/strong>\u00a0at least regionally suppress plankton biomass and productivity<\/em><\/p>\n\n\n\n

For an organism, relocation or adjustment to osmotic and ionic stress\u00a0may<\/strong>\u00a0be energetically costly<\/em><\/p>\n\n\n\n

Such species\u00a0could<\/strong>\u00a0be affected by the\u00a0projected<\/strong>\u00a0end of the century salinity changes (~0.5\u20131.0 psu)<\/em><\/p>\n\n\n\n

It is of particular interest to understand which species are predicted to be the salinity change \u2018losers\u2019, as these\u00a0may<\/strong>\u00a0lead to altered or, in the most extreme case, loss of entire ecosystem functions.<\/em><\/p>\n\n\n\n

While quantitative data are lacking, such short-term salinity variations\u00a0may<\/strong>\u00a0well pose a larger pressure on coral than the more consistent, long-term ocean scale salinity changes<\/em><\/p>\n\n\n\n

Future shifts in salinity due to ice cap melting, precipitation variability, and SLR has the\u00a0potential<\/strong>\u00a0to alter global biogeochemical cycling, the effects of which are\u00a0likely<\/strong>\u00a0compounded by further climate change<\/em><\/p>\n\n\n\n

For the nitrogen cycle,\u00a0projected<\/strong>\u00a0increases in nitrogen mineralization and reduced coupled nitrification\u2013denitrification\u00a0could<\/strong>\u00a0result in increased NH4<\/sub>+<\/sup>\u00a0export from groundwater systems<\/em><\/p>\n\n\n\n

Along the estuarine continuum, freshwater tidal and upland ecosystems\u00a0may<\/strong>\u00a0be the biggest \u2018losers\u2019 connected to changes in salinity.<\/em><\/p>\n\n\n\n

Projected<\/em><\/strong>\u00a0salinity changes on the order of ~0.5 to 1.0 psu until the end of the century in conjunction with increased short-term variations due to precipitation and runoff pattern changes are\u00a0anticipated<\/strong>\u00a0to lead to ecotone (i.e., transition areas between communities) or ecosystem shifts<\/em><\/p>\n\n\n\n

Encroachment of halophyte species into fresher areas as saltwater reaches upstream\u00a0may<\/strong>\u00a0initially cause diversification of species at the ecotone and be an advantage to brackish taxa.<\/em><\/p>\n\n\n\n

These regions are\u00a0likely<\/strong>\u00a0to undergo the most dramatic changes in salinity reduction and enhanced stratification<\/em><\/p>\n\n\n\n

Salinity and inundation stress\u00a0may<\/strong>\u00a0also create a positive feedback loop for tidal wetlands at large, whereby stress and low reproduction leads to increased plant death and decay and decreased net carbon inputs, which then cause soil compaction and subsidence.<\/em><\/p>\n\n\n\n

These responses\u00a0may<\/strong>\u00a0be influenced by any combination of physiological osmoacclimation and phenotypic plasticity (i.e., variation within strains), genetic variation among strains, and evolutionary osmoadaptation<\/em><\/p>\n\n\n\n

We therefore applied distribution modeling to explore the effects of open ocean near-surface salinity changes on coral habitat suitability. Our models indicate pronounced responses to\u00a0projected<\/strong>\u00a0salinity changes.<\/em><\/p>\n\n\n\n

In certain cases, [harmful algae blooms]\u00a0may<\/strong>\u00a0be induced by salinity changes<\/em><\/p>\n\n\n\n

The ensuing shift to asexual reproduction promotes lower genetic diversity and\u00a0may<\/strong>\u00a0consequently impair the potential for adaptation to new selective marine regimes<\/em><\/p>\n\n\n\n

Increasingly hyposaline conditions of the Baltic Sea\u00a0may<\/strong>\u00a0also cause a shift toward the prevalence of green algae<\/em><\/p>\n\n\n\n

Climate model future\u00a0projections<\/strong>\u00a0(of end of the century salinity changes) indicate magnitudes that lead to modification of open ocean plankton community structure and habitat suitability of coral reef communities.<\/em><\/p>\n\n\n\n

As wetland hydrology and seasonal rainfall patterns continue to change, die-offs in these areas\u00a0may<\/strong>\u00a0very well increase in frequency and coverage<\/em><\/p>\n\n\n\n

By the end of the century, near-surface changes are\u00a0projected<\/strong>\u00a0to increase markedly, by an order of ~0.5 to 1.0 psu, and in the deep by about 0.05 psu.<\/em><\/p>\n\n\n\n

Aquaculture\u00a0may<\/strong>\u00a0further be directly impacted<\/em><\/p>\n\n\n\n

Salinity-triggered changes to global ocean currents (including the THC) and enhanced stratification\u00a0may<\/strong>\u00a0provide direct feedback on the rate of climate change, but the direct and indirect consequences on human socioeconomics remain difficult to quantify.<\/em><\/p>\n\n\n\n

Accordingly, biodiversity shifts are\u00a0projected<\/strong>\u00a0as a result of salinity changes due to diversification within new niches<\/em><\/p>\n\n\n\n

Existing research typically does not address spatial, diel, monthly, and seasonal variability of salinity. Enhanced short-term variability through extreme events (e.g., droughts, floodings)\u00a0may<\/strong>\u00a0well impose a stronger selective pressure on ecosystems than long-term changes<\/em><\/p>\n\n\n\n

Future projections using the previous CMIP5 model suite are indicating these currently observed changes are\u00a0likely<\/strong>\u00a0to intensify<\/em><\/p>\n\n\n\n

This review highlights that detailed data on the effects of salinity changes on the vast majority of ecologically and economically important ecosystems are lacking, which makes the\u00a0projection<\/strong>\u00a0of consequences highly inaccurate<\/em><\/p>\n<\/blockquote>\n\n\n\n

Aaargh! Enough with the\u00a0projections<\/strong>\u00a0of\u00a0potential<\/strong>\u00a0and\u00a0may<\/strong>\u00a0and\u00a0might<\/strong>\u00a0and\u00a0could<\/strong>! Not one of them is falsifiable, they all might happen \u2026 and?<\/p>\n\n\n\n

Yes,\u00a0projections<\/strong>\u00a0could<\/strong>\u00a0indicate the\u00a0potential<\/strong>\u00a0that it\u00a0may<\/strong>\u00a0be possible that I\u00a0might<\/strong>\u00a0win the lottery \u2026 but I\u2019m not planning on using my potential lottery winnings for my retirement based on weasel words.<\/p>\n\n\n\n

So, I decided to see what I could learn about salinity. Despite a life spent near, on, or in the ocean, despite spending years commercial fishing and\u00a0ocean sailing<\/a>\u00a0and surfing and diving, my knowledge of the vagaries of ocean salinity at the start of this inquiry was \u2026 well, let me call it unimpressive and leave it at that.<\/p>\n\n\n\n

In fact, most of what I knew of ocean salinity came from Izak Dinesen, who said:<\/p>\n\n\n\n

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The cure for anything is salt water\u2014sweat, tears, or the sea.<\/em><\/strong><\/p>\n<\/blockquote>\n\n\n\n

That\u2019s worked for me for my whole life, but I didn\u2019t know, for example, whether the Atlantic is saltier than the Pacific (turns out it is). So I went about doing what I love to do \u2026 my homework on a subject where I know very little. Science for me is about the joy of learning.<\/p>\n\n\n\n

It turns out that you can measure the salinity of the ocean from satellites. Who knew? Certainly not me. However, as is far too often true, they don\u2019t make getting the data easy. In this case, I merely had to download 138 separate monthly NetCDF files, open each NetCDF file, extract the data for each month, resample that data to 180\u00b0 latitude by 360\u00b0 longitude, and create a 180 latitude x 360 longitude x 138 month array of the results where each layer in the array is a monthly global map of the salinity.<\/p>\n\n\n\n

Easy money, right?<\/p>\n\n\n\n

And at the end of that small matter of programming, here\u2019s the average satellite-measured salinity over the recent period. Salinity is measured in \u201cpractical salinity units\u201d, or \u201cpsu\u201d.<\/p>\n\n\n\n

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Figure 1. Average sea surface salinity.<\/em><\/figcaption><\/figure>\n\n\n\n

The global average is 34.6 psu, but there is some variation. Most of the globe is between ~ 32 and ~36 psu. The lowest surface salinity is in the Arctic, highest is in the Mediterranean. You can see the effect of the rainfall lowering the salinity in the Inter-Tropical Convergence Zone (ITCZ) in the Pacific above the Equator.<\/p>\n\n\n\n

Next, I looked at how much the salinity in each gridcell changes over the course of the year.<\/p>\n\n\n\n

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Figure 2. Average annual range sea surface salinity.<\/em><\/figcaption><\/figure>\n\n\n\n

In Figure 2, we can see that the average annual swing from highest to lowest salinity is about 1 psu. In general, swings are higher in the tropics and on the eastern temperate coasts of the continents.<\/p>\n\n\n\n

How about the trends in salinity? Here, we need to be cautious because we only have a bit more than a decade of data. I\u2019ll return to that issue in a bit. For now, here are the decadal trends in salinity.<\/p>\n\n\n\n

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Figure 3. Decadal trends in sea surface salinity.<\/em><\/figcaption><\/figure>\n\n\n\n

Note that the trends are very tiny. In addition, there\u2019s a curiosity about them. They are far from being normally distributed. They most closely follow what\u2019s called a \u201cCauchy\u201d distribution. Here\u2019s the distribution of the gridcell-by-gridcell salinity trends shown in Figure 3.<\/p>\n\n\n\n

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Figure 4. Histogram showing the distribution of the sea surface salinity decadal trends in black. Best-fit Cauchy and Normal distributions are also shown.<\/em><\/figcaption><\/figure>\n\n\n\n

Although the range of the average swings in annual sea surface salinity for the ocean is 1 psu, we\u2019re supposed to get all excited about a possible change of a tenth of a psu or less \u2026<\/p>\n\n\n\n

So that\u2019s the short-term view of salinity. However, we do have some longer observational datasets for both the surface and deeper ocean. These are collated by the UK Met Office Hadley Centre, and are entitled \u201cEN4: quality controlled subsurface ocean temperature and<\/a>\u00a0<\/a>salinity profiles<\/a>\u201c.<\/p>\n\n\n\n

Here are those salinity datasets, which cover from 1900 to 2019 on a monthly basis.<\/p>\n\n\n\n

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Figure 5. Long-term changes in surface and deeper salinity.<\/em><\/figcaption><\/figure>\n\n\n\n

Now I\u2019m sure folks will scream that I\u2019m minimizing the trends by using a zero-based graph \u2026 but look at the trends. The surface trend is the largest, and it\u2019s only 0.013 psu per century. Not per decade. Per century, during a century of general warming.<\/p>\n\n\n\n

However, for those who want it, here\u2019s a close-up of the surface salinity. To avoid misrepresenting the situation, however, I\u2019ve expressed the changes as deviations from the mean value of the total dataset.<\/p>\n\n\n\n

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Figure 6. Long-term changes in surface salinity, closeup view.<\/em><\/figcaption><\/figure>\n\n\n\n

Note that even including the seasonal variations, the global average sea surface salinity has only varied about \u00b1 0.2% over the entire period, and in 2019 we were back right about where we started.<\/p>\n\n\n\n

Finally, how do the long-term and short-term datasets compare? Unfortunately, there\u2019s not a lot of overlap, but given that it\u2019s the world of climate datasets, the agreement is not bad. It does show us why the long-term trend from the EN4 dataset is slightly positive, while the short-term trend from the OISST dataset is negative.<\/p>\n\n\n\n

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Figure 7. Overlap period, short- and long-term sea surface salinity datasets. Changes are shown as percentage variations from the mean.<\/em><\/figcaption><\/figure>\n\n\n\n

So \u2026 that\u2019s what I learned today about salinity.<\/p>\n\n\n\n

TL;DR version?<\/p>\n\n\n\n