GEOFF BENNETT: As the Trump administration pulls back from regulations on climate change, many scientists remain worried about the warming of the oceans, glaciers and sea level rise.

Our science correspondent, Miles O'Brien, has been reporting from Antarctica on a major mission to understand what's happening there.

In his latest report from the Thwaites Glacier, he looks at other key research projects that have been part of that trip.

MILES O'BRIEN: The timing was awkward.

New York University glaciologist David Holland and I landed on the Thwaites Glacier almost precisely when the valiant effort to bore through it and install a suite of sensors in the ocean beneath reached an unceremonious dead end.

MAN: Stuck.

DAVID HOLLAND, New York University: We did not succeed in doing what we wanted to do, was to put a weather station in the ocean out there to begin to monitor it.

What we achieved there was nothing, absolutely nothing, a little bit Shakespearian.

MAN: Damn, that's brutal.

MILES O'BRIEN: The tragedy became comedy when Dr.

Holland asked me to give him a hand, which, as an arm amputee, is literally all I had to offer.

But I have a hard time saying no.

OK, these are empty.

Just my speed.

All right.

Let's go!

What are you doing?

Are you doing your end?

DAVID HOLLAND: That's dragging.

No, I think that one is just dragging.

MILES O'BRIEN: All right.

So we started setting up the distributed temperature sensor, the last instrument slated to go down the hole.

The heavy gear connects to a fiber-optic cable that provides continuous temperature readings from the surface to the seafloor.

But now it will come up about 650 feet short.

Once the hole closed up, you could have closed up shop and just come back to the ship, but you didn't.

DAVID HOLLAND: Why?

So it shows the possibility of what we can do in terms of remote instrumentation.

So it would be sugarcoating to say that's really great.

I would say that's better than nothing.

MILES O'BRIEN: The drill project was the marquee event of a monthlong scientific campaign launched from the deck of the icebreaker Araon owned by the Korea Polar Research Institute, or KOPRI.

Despite the drilling failure, they notched some success.

One of the helicopters flew for several days over the ice, surveying with a powerful radar able to peer through the thick ice to measure it and see what the lay of the land is below.

Now in its sixth year, the research campaign is a partnership between KOPRI, the University of Texas, and Montana State University.

CHRIS PIERCE, Montana State University: So they have been out for, what, six hours now, a little over six hours.

MILES O'BRIEN: The field team leader is glaciologist Chris Pierce.

They logged more than 1,800 miles of straight lines up, down, and across the glacier over six flight days.

The trio of long booms contains the radar antennas.

They send long wavelength radio signals downward and then listen for the echoes.

The elapsed time of their return defines details beneath the surface.

CHRIS PIERCE: We have got really good-quality data and we have got really good coverage coming out of this.

MILES O'BRIEN: He showed me one of their radargrams.

It's a two-dimensional slice of the ice, like an MRI or X-ray, understanding the terrain beneath the ice is a priority for researchers, developing models to predict how fast the glacier might retreat.

CHRIS PIERCE: Once you get past a certain point, you're going to have a really, like, low-friction surface on which the glacier can slide.

So that's one of the reasons that people believe that Thwaites is particularly susceptible to instabilities.

MILES O'BRIEN: To help calibrate his radar, Pierce turns to sea ice scientist Siobhan Johnson of the British Antarctic Survey to get a precise read on the density of firn, snow that is transitioning to ice.

She is an expert in ice coring.

We were on top of Thwaites when she showed me how it's done.

So, a little easier than doing it manually.

SIOBHAN JOHNSON, British Antarctic Survey: Yes.

Yes.

MILES O'BRIEN: So, let's give it a try and see how it goes.

SIOBHAN JOHNSON: Yes?

MILES O'BRIEN: She uses a coring device attached to a cordless drill.

Easy peasy.

This core represents about six months of firn.

It tells a story if you know how to read it.

Clear ice means a warm spell.

SIOBHAN JOHNSON: Oh, actually you see a little here.

MILES O'BRIEN: Oh, yes?

SIOBHAN JOHNSON: It's got some melt layer.

Do you see?

MILES O'BRIEN: Oh, yes, I do.

I do.

When she cores sea ice, she cuts a precise section, then weighs it to determine its density.

In 2016, sea ice here began a sharp and unexpected drop as the climate crisis changes wind and ocean currents.

Melting sea ice does not directly raise sea level since it's already floating.

But its loss can indirectly accelerate the melting of land ice, glaciers like Thwaites.

SIOBHAN JOHNSON: The cover of the sea ice in this area is quite important for ocean heat transport, which will melt the underside of the Thwaites.

MILES O'BRIEN: The role of sea ice in glacier melt forecasts is one of a myriad of uncertainties this expedition was designed to help unravel.

The team deployed and recovered moorings that collect underwater data profiles over multiyear periods.

They made frequent stops to measure the ocean's salinity, temperature, depth, currents, and chemical composition.

And they launched and retrieved an autonomous underwater glider carrying profiling instruments on a multiday mission.

But perhaps the most novel approach was this, a device called RIFT-OX.

Polar geophysicist Jamin Greenbaum of the Scripps Institution of Oceanography at U.C.

San Diego, teamed up with helicopter maestro Dominic O'Rourke to fly into ice canyons on a series of daring missions.

JAMIN GREENBAUM, Scripps Institution of Oceanography: So, at Thwaites, we can take advantage of the fact that it's collapsing and producing these rifts that allow you to get to places that in other glaciers you just can't get to.

MILES O'BRIEN: RIFT-OX is lifted by helicopter and flown to a fractured rift.

It breaks through thin ice and lowers a rosette of canisters as deep as 2,800 feet.

They capture water samples at prescribed depths.

They're looking for telltale signs of subglacial discharge.

Formed under the glacier by geothermal heat and friction as the ice slides over the rock, it squirts into the sea, where it mixes with warm ocean water.

JAMIN GREENBAUM: You know, I like to think of the warm ocean as like the fire.

And this subglacial discharge, I like to think of it like lighter fluid that's getting sprayed into the fire, and it just -- it just blows the whole thing up.

MILES O'BRIEN: His early data have confirmed this hypothesis.

JAMIN GREENBAUM: And, lo and behold, in area three we see direct evidence of subglacial discharge.

So it really is exactly where we thought it might be.

MILES O'BRIEN: Wow.

It's all hard-won data.

KOPRI is vowing to return in two years.

The puzzle pieces are elusive and the hard work here moves at the pace of a glacier.

But this one, the most consequential of them all, is moving faster than efforts to understand it.

For the "PBS News Hour," I'm Miles O'Brien at the Thwaites Glacier.