New analysis highlights importance of groundwater discharge into oceans

From UC Santa Cruz News Center

A global assessment of the impact of groundwater on ocean chemistry is important for understanding the weathering of rocks and its effects on climate

January 08, 2021

By Tim Stephens

Coastal groundwater discharge can sometimes be seen at low tide as rivulets flowing into the ocean, as on this beach on Oahu. (Photo by Jenny Bernier)
Groundwater discharge flows through the sand on an Oahu beach. A global assessment found groundwater discharge plays a more significant role in ocean chemistry than had been thought. (Photo by Jenny Bernier)
Kimberly Mayfield prepares groundwater samples for lithium isotope analysis in a clean lab at the Czech Geological Survey in Prague. (Photo by Tomas Magna)

An invisible flow of groundwater seeps into the ocean along coastlines all over the world. Scientists have tended to disregard its contributions to ocean chemistry, focusing on the far greater volumes of water and dissolved material entering the sea from rivers and streams, but a new study finds groundwater discharge plays a more significant role than had been thought.

The new findings, published January 8 in Nature Communications, have implications for global models of biogeochemical cycles and for the interpretation of isotope records of Earth’s climate history.

“It’s really hard to characterize groundwater discharge, so it has been a source of uncertainty in the modeling of global cycles,” said first author Kimberley Mayfield, who led the study as a graduate student at UC Santa Cruz. “It took a large effort by researchers around the world who came together to make this happen.”

The researchers focused on five key elements—lithium, magnesium, calcium, strontium, and barium—measuring concentrations and isotope ratios in coastal groundwater at 20 sites around the world, and using previously published data from additional sites.

“Those elements are important because they come from the weathering of rocks, and weathering of silicate rocks accounts for a huge uptake of carbon dioxide from the atmosphere over long time scales,” Mayfield explained.

Coauthor Adina Paytan, a research professor in UCSC’s Institute of Marine Sciences, said groundwater is an important source of inputs to the oceans, but has been easy to ignore because it is unseen and hard to measure.

“This is the first global assessment of groundwater discharge for most of these elements,” Paytan said. “This information is useful for our understanding of how weathering of rock is related to climate, not only in the present but also in the past.”

Full article here

4.6 7 votes
Article Rating
Newest Most Voted
Inline Feedbacks
View all comments
January 11, 2021 10:05 pm

Groundwater seeps along the beaches of Cairns, GBR, are huge … bubbling up through the sand when the tide is down !

January 11, 2021 10:09 pm

All rainfall eventually reaches the sea.

Mr. Lee
January 11, 2021 10:35 pm

is an important source of inputs to the oceans, but has been easy to ignore because it is unseen and hard to measure

Yeah, that’s what we do in physics too…if it’s too small to see or hard to measure, we ignore it. It just seems easier that way \sarc

January 11, 2021 10:52 pm

This sounds like an interesting study.

I wonder where “climate change” comes into it to get the funding ? 😉

Finding out where water goes to, is actually quite important as an engineering problem.

Take Perth for instance, they know the aquifers they can take water from are linked to the sea, that is why they have to be very careful how much they take out (or put back in.)

I suspect they will go with more desal plants as Perth expands, rather than messing with the groundwater too much, even though it would cost more to do desal plants..

Reliability vs cost vs risk…

Joel O’Bryan
Reply to  fred250
January 12, 2021 12:21 am

jumping on the climate gravy train to grant success regardless of whether CC is relevant to the field’s questions.

Stephen Skinner
Reply to  fred250
January 13, 2021 12:34 am

Finding out where water goes to, is actually quite important as an engineering problem.”
Of course and all water flows down hill.

January 11, 2021 11:06 pm

I wonder if this assessment has also looked at nitrate/nitrite contaminated groundwater.

Peta of Newark
January 12, 2021 12:48 am

“”This information is useful for our understanding of how weathering of rock is related to climate””

Well yesssss, but you need to take one more step.

This obviously links (quite) nicely to my endless ravings about Soil Erosion ##
It points to the question that I always ask of people who say “Oh, the climate changed, wiped out the civilisation and created the desert. Us sweet little humans were helpless to stop it”

I will always demand to know: “Where did all the sand come from?

Check out the Wiki and it is there – the Silica Sand is all that’s left after the weathering.
Most especially and as they say here, all the things disolved out of the rock are the macro and micro nutrients that plants need and use.
When those nutrients are all weathered aaway, the plants die and you have a desert left behind
And when the plants go, the weather/climate goes crazy.
Buried organics created by the plants are oxidised, CO2 is released in large amounts and no plants are there-absorb it. That doesn’t matter. Not one jot.

What does matter to weather/climate was all the water that did used to be retained in the soil by the buried organics.
That water-store controlled the weather/climate.
Just like The Ocean does with its huge thermal inertia.

Even before each molecule (Cellulose mostly) of the stuff comprised equal numbers of carbon atoms and water molecules. Where does that water go?

And what does farming and agriculture (Tillage generally) do – it weathers the soil.
ESPECIALLY nitrogenous fertiliser

Is The Picture starting to come together.
It fits perfectly and the timing is also perfect.
Check the graphs and see that the ramping up of atmospheric CO2 really kicked off just after WW2 – when large amounts of nitrate, under Governmental direction/mandate – started to be used on farmland.
Kicked up another gear with the Green Revolution = the development of ‘miniature’ high yielding varieties that responded much better to high nitrogen inputs.

It’s not The Industrial Revolution that kicked off the observed Climate Change – it was/is The Agricultural Revolution. i.e. Nitrogen fertiliser and the plants that use it

I keep repeating “We are on the cusp of something so dumb that we extinguish ourselves

Maybe we already did it and are accelerating down that road – we did it at end of WW2

## The Wiki refers to Soil Erosion as the actual physical removal of rocks, soil, dust, dirt etc from a landscape.
I don’t and do subscribe to that.
I class, as do many others, what they call ‘Weathering’ as = Erosion also.
But in two different flavours – Chemical and Physical Erosions

Peta of Newark
Reply to  Peta of Newark
January 12, 2021 1:21 am

I didn’t say how nitrogen fertilser weathers the farmland soil and in fact, how it actually does make the plants grow bigger better faster.
(The reason has been known since it first became available – it was originally supplied to farms as Calcium Nitrate – not Ammonium Nitrate as it is now)

The Nitrate primarily feeds soil bacteria. THAT is why, as farmers know, it is entirely pointless applying nitrate at soil temperatures of 5 Celsius or less.
(The temperature of your fridge, completely NOT coincidentally)

Nitrate is the Liebig Limiter for the bacteria and when they get some extra, they go crazy eating.digesting whatever they can within the soil. Ancient cellulose in its various states of decay
Just as when you make beer or wine, sugars become alcohols and then, after further oxidation, become acids. Vinegar as in the case of (ethyl alcohol) from beer & wine.

And it is those organic acids that do far more weathering than atmospheric CO2 ever did, releasing vastly more of the (now) water soluble nutrients that the plants need.
Which the plants suck up with their roots obviously.

The Clear Headed Thinker will now realise why plants, seemingly responding to elevated CO2 levels, require less water.
Higher nutrient levels in the soil simply mean they need to suck up less to get what they need.
And why when NASA tell us that extra CO2 is causing Global Greening, we know that they’ve really rather completely, Lost The Plot.

Think about it also. As the article here says, CO2 dissolves in water. Carbonic Acid.
Plants make, initially glucose sugar, equal numbers of carbon atoms to water molecules.
So why don’t the plants get sufficient sugar-building water from the CO2 they’re absorbing, which must be coming in as Carbonic Acid
Is that why there is a Magnesium atom at the centre of each Chlorophyll molecule?
Magnesium being of very similar chemistry to the Calcium they’re talking about here

So, next time we see Old What’s His Name with the 3 Xmas trees, we can all just shake our heads at his Magical Thinking and how he did such a poor experiment – one that confirmed his biases. Ones that he was taught at primary school and oft-repeated around here.

A bit sad really innit

Reply to  Peta of Newark
January 12, 2021 2:52 am

 –Vinegar as in the case of (ethyl alcohol) from beer & wine–

The problem of acetobacter. If you aren’t thorough in [production] cleaning processes they can really mess things up, but thankfully nowhere near as badly as zymomonas.

That’s a shut down and deep clean situation.

David A
Reply to  Peta of Newark
January 12, 2021 12:56 pm

“why when NASA tell us that extra CO2 is causing Global Greening, we know that they’ve really rather completely, Lost The Plot.”

Um, sorry but no. They are correct.

Reply to  Peta of Newark
January 12, 2021 4:58 am

“When those nutrients are all weathered aaway, the plants die and you have a desert left behind”

Nope. If there is enough water plants will grow even in pure silica sand, admittedly it will be pretty poor, slow-growing and quite specialized vegetation, like the arena blanca in the Amazon:

Or the Northern European “tallmo” (pine heath):

comment image

By the way very large areas in Australia is extremely weathered since the landscape is very old and the continent was situated in wet temperate climates for a couple of hundred million years. Some areas are so poor in nutrients that grazing animals get deficiency diseases

January 12, 2021 2:28 am

-a source of uncertainty in the modeling-

Just one of many.

-easy to ignore because it is unseen and hard to measure-

That’s modelling for you. If it’s difficult, ignore it or make it up.

January 12, 2021 3:27 am

If a tree falls in the forest and nobody hears it, does it effect climate change?

January 12, 2021 5:03 am

I wrote of this as Reason #23 in
Chill: 49 Reasons to Worry Less About Climate Change.

Groundwater mining continues to accelerate.

January 12, 2021 5:51 am

Groundwater is worse than we thought.

January 12, 2021 6:17 am

Such groundwater seepage can be quite noticeable in arid areas where there is no surface water, but where coastal inlets can have brackish water because of the groundwater discharge. The classic case is the “Khors” or “Khawrs” of Arabia where the landward ends of the inlets are almost fresh with reed-beds and the outer parts have mangroves, while the country around is completely dry and vegetationless.

In some places on the southern coast of the Persian Gulf early travellers describe how people used to dive with empty water containers and fill them from subsurface freshwater springs.

very old white guy
January 12, 2021 6:30 am

Scheesh, I guess natural occurrences now can be controlled if only we study them more. Falls under the heading, turn down the sun and we will eliminate global warming, or whatever.

H. D. Hoese
January 12, 2021 6:39 am

I have drunk ‘potable’ water next to a salty sea from shallow wells dug in sandy barrier islands and they have been long a necessary source. In places freshwater plants like cat-tails grow where open water salinities are higher than their tolerance. Sometimes there are septic systems. Florida has a number of significant offshore springs, paper has sample, related to aquifers and rainfall. Coastal lithology they mention–“ However, no lithologic weighting was considered in this model. In lieu of lithologic weighting, we opted to take the average of the final chemical compositions of global groundwater discharge calculated via the geologic weighting in the other two models: Beck et al.4 and Luijendijk et al.2 and simply multiply by the Zhou et al.1 flux.” Different lithology here–Bratton, J. F., J. K. Böhlke, D. E. Krantz, and C. R. Tobias.2009. Flow and geochemistry of groundwater beneath a back-barrier lagoon: The subterranean estuary at Chincoteague Bay, Maryland, USA. Marine Chemistry.113(1-2):78-92.

Sometimes it is not so fresh and has other uses–Forsberg, J. A. and W. H. Neill. 1997. Saline groundwater as an aquaculture medium: physiological studies on the red drum, Sciaenops ocellatus. Environmental Biology of Fishes. 49:119-128.

Clyde Spencer
January 12, 2021 11:25 am

Little did I realize that if I were ship wrecked on a desert island, and needed drinking water, all I would have to do is go down to the beach at low tide and drink from the rivulets! /sarc

Nowhere is there mention of the salinity of the claimed ‘fresh water’ shown in the photographs or of the sampled water. There are situations, such as areas with high rainfall, and and water tables near the surface, where fresh water may be showing up in beach sands. However, for places such as the Atacama desert or the Namib desert, I would expect any water from inland reaching the ocean would not be close to the surface! How did the researchers sample those inflows to get representative global samples? Even places that have Mediterranean climates, with almost no Summer rainfall, I wouldn’t expect those beach rivulets to be potable water. My expectation is that what one would typically see on the beaches in the Summer in California would be water draining out from the last high tide or the infrequent large waves that make it high up the beach.

David A
Reply to  Clyde Spencer
January 12, 2021 1:47 pm

I have live in Southern California all my life. All along the coast where there are cliffs you will see year round water coming out of the cliffs.

Clyde Spencer
Reply to  David A
January 12, 2021 8:00 pm


Yes, and you will find springs (oases) in deserts. That doesn’t imply that the water table is intersected by the oasis or the beach. More likely what you are observing in the cliffs — usually distinguished by green algae and/or iron-oxide staining — is either what is called a perched water table, or a fracture system that water can follow, and having a point of infiltration at higher elevation, which provides a hydraulic head to force the water through the fractures. The pictures in the article imply sheet flow that is intersected by the beach. Possible, but probably only common in areas of high rainfall. Associated conditions that would distinguish the situation would either be shallow wells that can be dug, or artesian wells intersected by shallow drilled holes.

January 12, 2021 3:07 pm

You don’t have oysters without ground water seeps onto the beach. The basin where I keep my boat has so strong a fresh water outflow that given that fresh water flows on salt water, my water level exhaust always has oyster starts every year that I have to clear out.

Clyde Spencer
Reply to  EJW
January 12, 2021 8:04 pm

It would be helpful is you stated where you live. Are these freshwater oysters, or a species that likes brackish water? Note that I did not state that such a situation is impossible. However, the article seems to imply that is the usual situation.

January 12, 2021 5:02 pm

About the photographs of groundwater emerging at beaches, there are lots of places along the coast of Oahu where streams have become blocked by sand. Here is one Mākaha Beach Park – Google Maps . Here is another Honolulu – Google Maps

Convince me that this “groundwater seepage” emerging from beach sand/gravel isn’t just water flowing from such a blocked-up river?

Clyde Spencer
Reply to  JCalvertN(UK)
January 12, 2021 8:07 pm

It may well be river water that has to pass through a barrier to get to the ocean. But, I wouldn’t consider that to really be ground water. Further, it is localized near the mouth of the river, and not sheet-flow representing groundwater from a high water table.

January 12, 2021 7:13 pm

The pictures appear to be taken at Ala Moana beach near downtown Honolulu.
The entire area – including the fake beach, was built on dumped material (mostly coral) from the dredging of Pearl Harbour.

So, the whole area is built on highly permeable material. When the tide rises, sea-water permeates into the fill underlying the whole area. Then when the tide falls, the sea-water permeates out again.

No “groundwater” involved.

Clyde Spencer
Reply to  JCalvertN(UK)
January 12, 2021 8:19 pm

I have frequently seen summertime lagoons on northern California beaches near the mouth of a stream. There may or may not be an outlet to the lagoon. But, the sands downslope are saturated with warm, brackish water. If one wants to characterize the chemistry of groundwater supplying ions to the ocean, then the true groundwater should be sampled and not water from surface streams (which are already monitored by the USGS in the states), which happen to move a short distance through sands that are periodically soaked in salt water.

Basically, I’m saying that, based on the article, it appears to me that the experiment was poorly designed. However, I’m sure they enjoyed their time in Hawaii!

Reply to  Clyde Spencer
January 13, 2021 9:08 pm

They would have enjoyed their time in Hawaii quite a lot more, if they had ventured a bit further afield than the Ala Moana fake beach!

Verified by MonsterInsights