In the 1970s, our understanding of what's necessary for life itself was turned on its
head with the discovery of hydrothermal vents.
Deep on the sea floor among huge pillars, spilling super-heated, chemical-rich fluid
scientists found lifeforms that don't require sunlight to exist, something previously thought
to be impossible.
Instead of sunlight and photosynthesis, the base of the food chain at these vent ecosystems
was chemosynthesis or the production of food, using energy released by inorganic chemical
reactions.
But vents aren't the only ecosystems that can support chemosynthetic communities.
Once scientists knew what to look for, they found them in hot springs on land, on the
seafloor around whale carcasses and sunken chips, and in association with cold seas around
the world.
Cold seas are places where chemical rich fluids and gases escape from fissures in the ocean
floor.
Unlike hydrothermal vents, which are fueled by geothermal activity, the seepage of these
sites is fueled by immense pressure.
Also, in contrast vents, there isn't a strong increase in temperature relative to the surrounding
waters.
The chemicals that emerge from seas are toxic to most forms of life.
However, these chemicals, most importantly, hydrogen sulfide, methane, and other hydrocarbons
actually provide the building blocks for entire chemosynthetic ecosystems.
At the base of the food web are chemosynthetic microbes, some that live freely and some of
which live symbiotically within other organisms.
Longer lasting and more stable in their vent counterparts, seeps can persist for decades,
centuries, and likely even millennia before subsiding, but they don't last forever.
Over time, the toxic flow lessons and stops entirely, and the ecosystem is settled by
new species.
From both a geological and ecological perspective cold seats are prime sites for new questions
and answers, and then often more questions.
To learn more, let's talk to an expert.
Today we're joined by Melissa Betters, a PhD candidate from Temple University whose interests
lie in the evolutionary origins of chemosynthetic organisms at cold seeps.
Welcome Melissa.
Thanks for being with us today.
Hi, Liz.
Thank you for having me.
So cold seeps occurred globally, correct?
Where exactly are they found and how do they form?
Cold seeps are found all around the world in every ocean.
They're found along continental margins.
One place you can find them is at subduction zones where one plate is sliding underneath
another plate.
When that happens, that underlying plate is undergoing a massive amount of pressure, just
like a sponge.
All of the fluids and things contained in the sediment of that plate get expelled into
the water column, and that's where we get seeps.
I really like that sponge analogy, but what exactly does that look like on the sea floor?
So the way the cold seeps, uh, look, when you're actually down there is pretty magnificent.
In a lot of cases ou get these really amazing bubble plumes, which is all of these hydrocarbons
kind of bubbling up from the sediment, which create, uh, What looks like reverse waterfalls.
Otherwise you get what we call shimmering water, which is where the water is slightly
warmer than ambient.
Um, and you get this really beautiful shimmering effect.
But of course, there's a huge diversity of ways that cold seas can look.
Can you tell us a little bit more about that diversity.
What other forms of cold seeps are there?
I work on hydrocarbon seeps specifically, but there are also seeps such as salt seeps
that form, brine pools, which are essentially these pools of really salty water that comes
up from the sediment.
And this salty water is actually too salty.
It can't mix with the overlying ocean water.
And so it forms into these beautiful pools.
Uh, you also get really dramatic formations, such as Tar Lilys, where you have these hard
structures kind of solidifying once they seafloor.
Wow.
I didn't realize there were so many types of cult seeps out there.
Can you tell us a little bit more about what exactly is being extruded at seep sites?
Yeah, so there are a bunch of different chemicals that tend to be extruded at these seep sites.
We tend to focus mainly as biologists on hydrogen sulfide and the hydrocarbons.
So those are things like natural gas and methane.
And the reason why is that hydrogen sulfide and methane can be used by the animals at
these sites to actually fuel the ecosystems that we find there.
So how exactly do these complex ecosystems form in the first place?
Once methane and hydrogen sulfide start exuding from the sea floor, microbes tend to come
in that are able to turn those chemicals coming up from the sea floor into energy.
And once these microbes come and take hold, you have a lot of biological processes going
on, one of which creates what we call carbonate rock.
And that creates a hard surface on what would otherwise be bare sand.
And once you have that hard surface, other animals can start coming in and colonizing
that area.
Oh, I'm so glad you mentioned the animals.
I'm hoping you can tell us a little bit more about the diversity that cold seeps supports.
Cold seeps support, a huge diversity of life, and you wouldn't necessarily expect that,
right?
These are sites way down on the ocean floor.
They are at immense pressures, really cold temperatures, and to us what would be toxic
conditions.
But these cold seeps are highly diverse.
They host what we call foundational species, which are the species that form kind of the
three dimensional structure that other organisms can live in.
So these are things like tubewom bushes, mussel beds, clam beds, that all of the other little
critters at these sites can call their homes.
These organisms are really unique because they have a symbiotic relationship with chemosynthetic
microbes.
That means that the foundational species and the microbes benefit one another.
The microbes which live inside these foundational animals use the seep fluids to produce their
energy.
Which subsequently provides food for the animal.
The animal meanwhile gives the microbes a really comfortable place to live, free from
predators and grazers, like the snails that I study.
So can any animal come in and live at a cold seep?
So not every animal at the bottom of the ocean can live at a cold seep right away when seepage
starts, to most things, those are relatively toxic chemicals.
And so the only animals that can really start to live there are those animals that are specifically
adapted to those conditions, primarily the foundational species that I was talking about.
And then from there you have what we call ecological succession, which is where different
animals live at these sites at different points in time.
So over the lifespan of a cold seep, you have decrease in the amount of chemicals actually
coming up to the water column.
And so that changes the animals that can live there.
Near the end of a cold seep's life, that's where you can have animals that are typically
considered background species.
So things like deep-sea corals, deep-sea sponges, a variety of fish species that don't rely
on those chemicals for their source of energy.
And they can come in and start living at and around those cold seep environments.
It's both strange and wonderful to think about these complex ecosystems having their own
life cycles so far away from us.
Do they have any impact on our own lives?
So despite cold seeps being located, you know, miles offshore, miles beneath the surface
of the ocean, cold seeps are hugely important to our daily lives.
Keep in mind that these hydrocarbons exude from the sea floor naturally.
And these can also be known as greenhouse gases.
So if these hydrocarbons, such as methane, are able to make their way to the surface
of the ocean, they can make their way into our atmosphere and potentially exacerbate
greenhouse gas effects in our atmosphere.
And so the ecosystems at these sites essentially function to stop that from happening.
They sequester that carbon in their own little ecosystems and keep the hydrocarbons from
exiting into our greater atmosphere.
And so these cold seep animals play a vital role in both the health of our oceans, as
well as, the health of our atmosphere.
What questions about cold peeps are still unanswered?
There are so many unanswered questions out there.
The questions that are the most kind of interesting to me and to the scientific community is,
you know, understanding how these [00:10:00] cold seeps are resilient or fragile in the
face of potential disturbance.
Because as I said, these ecosystems have huge consequences for the state of our climate
and for our ocean.
And then also I'm interested in still understanding how they relate to other ecosystems that rely
on that chemosynthesis.
That's something that we are still trying to understand.
Melissa, thank you so much for being here today.
Thank you so much, Liz.
This has been a lot of fun.