Science

I noticed yesterday that a polynya had formed in front of the Ronne Ice Shelf over the last 2 weeks.

Screengrab from NASA Worldview 17 February 2017
Screengrab from NASA Worldview 17 February 2017

In that image it is about 27,000 kmin area.

I mapped the opening of the polynya from MODIS imagery over the last two weeks. There is cloud in the images but the opening of the polynya is fairly clear.

Formation of the Ronne Polynya 30 January to 14 February 2017.
Formation of the Ronne Polynya 30 January to 14 February 2017.

On 31 January 2017 there is no open water, but then over the 16 day period it opens to the ~27,000 kmin area. If you're eagle eyed you can see that there is thin frazil ice forming in the open water in front of the ice shelf at the end of the sequence.

So what caused it?

...continue reading

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Watching the sea ice extent this summer in Antarctica has been a bit surprising. The Antarctic sea ice extent has been tracking at record lows virtually the whole austral summer. We are very close now to the expected sea ice minimum, and this is where we are:

Antarctic sea ice extent 12 Feb 2017 & diff from mean 1989-93 on same day. Blues imply more ice and reds imply less compared with the mean.
Antarctic sea ice extent 12 Feb 2017 & diff from mean 1989-93 on same day. Blues imply more ice and reds imply less compared with the mean.

On the left is the sea ice extent from the DMSP satellite 12 February 2017, and on the right the difference between the mean sea ice extent on 12 Feb over the period 1989-93 and 12 Feb 2017. I chose this time period as the cycle has been generally quite stable from year to year.

The current sea ice extent is:

Antarctic sea ice extent. Downloaded from NSIDC 14 February 2017.
Antarctic sea ice extent. Downloaded from NSIDC 14 February 2017.

It's clear the sea ice over the summer 2016-17 is showing historic lows. But it's also clear from the sea ice extent above that there is little sea ice left to melt out before the summer turns. Where the sea ice remains - mainly in the Weddell Sea and along the coast of Wilkes Land it is clearly densely packed. If the winds change and the remaining sea ice is decompressed then the extent may fall some more.

This is an animation of the Antarctic sea ice extent from 1 January 2017 to 12 February 2017:

The Antarctic sea ice extent 1 January to 12 February 2017. Data from DMSP SMMI
The Antarctic sea ice extent 1 January to 12 February 2017. Data from DMSP SMMI

And finally the difference between the mean sea ice extent by day for the 5-year period 1989-1993 minus the concentration from 1 Jan to 12 Feb 2017. Blue shades imply an increased sea ice extent compared with a 5-year mean, and reds imply a decreased sea ice extent.

The difference between the mean sea ice extent by day for the 5-year period 1989-1993 minus the concentration from 1 Jan to 12 Feb 2017. Blue shades imply an increased sea ice extent compared with a 5-year mean, and reds imply a decreased sea ice extent.
The difference between the mean sea ice extent by day for the 5-year period 1989-1993 minus the concentration from 1 Jan to 12 Feb 2017. Blue shades imply an increased sea ice extent compared with a 5-year mean, and reds imply a decreased sea ice extent.

Not long until the Antarctic sea ice minimum.

The sea ice around Antarctic is currently still at an historic low. As usual I think it is good to look at a geographic perspective on the sea ice distribution. This is the sea ice concentration 22 January 2017 compared with the  1989-1993 mean on the 22 January.

RED shades = less sea ice than the 1989-93 mean on 22 January.

BLUE shades = more sea ice than the 1989-93 mean on 22 January.

The mean Antarctic sea ice for the years 1989-93 on 22 January, the sea ice concentration on 22 January 2017 and the difference between the two data sets. Blue shades imply more sea ice and reds imply decreased sea ice compared with the mean. The original data come from the DMSP SMMI data set at the NSIDC.
The mean Antarctic sea ice for the years 1989-93 on 22 January, the sea ice concentration on 22 January 2017 and the difference between the two data sets. Blue shades imply more sea ice and reds imply decreased sea ice compared with the mean. The original data come from the DMSP SMMI data set at the NSIDC.

The Amundsen Sea has very low sea ice

Amundsen Sea has very low sea ice in January 2017
Amundsen Sea has very low sea ice in January 2017

Probably for me the most striking feature is the extremely low sea ice concentration from Pine Island Bay through to the Ronne Ice Shelf - this is the Amundsen Sea. We are not going to see much more retreat of of the sea ice in this sector as it has already melted. I think it will stay open water until the freeze up begins some around the end of February. It would have been a great year to do ship based oceanography along that coast. I wonder if their could be an impact on ice shelf melt here. It is possible but as you can see from this article - it is water away from the surface and a few hundred metres deep that is in contact with the glacial ice in the Amundsen Sea Embayment, Overall this has to be a result of the recent El Nino, and is a follow on from the polynya events we saw hear in the late winter.

The Bellingshausen Sea has very relatively high sea ice

In contrast you can see it would not be a good year to be working in the Bellingshausen Sea.

Sea ice extent is currently relatively high in the Bellingshausen Sea.
Sea ice extent is currently relatively high in the Bellingshausen Sea.

Nevertheless, as expected, it was possible to finally relieve the British Antarctic Survey Rothera Base in January.

The Weddell Sea is a game of two halves

Sea ice in the Weddell Sea is now compressed against the Antarctic Peninsula
Sea ice in the Weddell Sea is now compressed against the Antarctic Peninsula

The Weddell Sea ice is at this stage in the summer is compressed against the Antarctic Peninsula. This means that there is heavier sea ice to the close to the Peninsula, and much lower sea ice than expected in the rest of the Weddell Sea. If you look at the MODIS Terra Image you can pick out a very sharp sea ice edge.

MODIS image from the TERRA satellite 23 January 2017. The sea ice edge in the Weddell Sea is very sharp.
MODIS image from the TERRA satellite 23 January 2017. The sea ice edge in the Weddell Sea is very sharp.

Shackleton would have been in trouble this summer if he was heading to Elephant Island.

Towards the annual Antarctic sea ice extent minimum.

We expect the sea ice to reach a minimum towards the end of February. Clearly there are places where there is no more sea ice to melt. Where sea ice is present, it is all down to winds over the next month. If they change and move the pack towards open water then - just as we have seen in the Arctic, the concentration could fall much lower. If the winds continue as they have then we could expect the extent fall to slowly as the seasonal melt continues.

Overall it is still to be likely a record breaking year in the Antarctic sea ice extent record.

Sea ice continues to be very low in the Arctic this winter. A geographical perspective always helps so here is the status of the sea ice concentration 18 January 2017 compared with the  1989-1993 mean on the 18 January.

RED shades = less sea ice than the 1989-93 mean on 18 January.

BLUE shades = more sea ice than the 1989-93 mean on 18 January.

The mean Arctic sea ice for the years 1989-93 on 18 January, the sea ice concentration on18 January 2017 and the difference between the two data sets. Blue shades imply more sea ice and reds imply decreased sea ice compared with the mean. The original data come from the DMSP SMMI data set at the NSIDC.
The mean Arctic sea ice for the years 1989-93 on 18 January, the sea ice concentration on18 January 2017 and the difference between the two data sets. Blue shades imply more sea ice and reds imply decreased sea ice compared with the mean. The original data come from the DMSP SMMI data set at the NSIDC.

A few interesting areas that caught my eye:

Geographic Areas in the Arctic with a strong absence of sea ice on 18 January 2017.
Geographic Areas in the Arctic with a strong absence of sea ice on 18 January 2017.

The first highlight region is the Northern Barents Sea. Sea ice has been very low here all winter, and this situation continues. Because the sea ice has been very late, the polar bears on Svalbard will be impacted, and it has been an issue in Longyearbyen....

Polar bears in Longyearbyen
Polar bears in Longyearbyen.

...continue reading

Project MIDAS publicised on Friday that a huge iceberg is going to calve from the Larsen C Ice Shelf. This was written up a a great story on the BBC news website Huge Antarctic iceberg poised to break away.  I understand a little about this stuff so got drawn into the media around it. Here is a BBC News interview on 6 January 2017.

It was great to see Antarctica in the news and it was brilliant to see so many high quality interviews from so many colleagues to different outlets. I may try and collate some of these in the next few days.

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The Arctic

It's been quite a year in the Arctic. Over the winter 2015/6 we had the strongest and coldest Arctic polar vortex of the last 68 years. This contributed to a low maximum in Arctic sea ice extent. At that stage only the locals and the scientists were looking, and I wrote about this in a blog post called Arctic sea ice 2016. This was followed by the joint second lowest Arctic summer sea ice extent.

Unusual weather in the early winter led to records being broken and the sea ice the Arctic sea has been the lowest recorded in the satellite record for the time of year.

Where are we at the Northern winter solstice?

The mean Arctic sea ice for the years 1989-93 on 21 December, the sea ice concentration on 21 December 2016 and the difference between the two data sets. Blue shades imply more sea ice and reds imply decreased sea ice compared with the mean. The original data come from the DMSP SMMI data set at the NSIDC.
The mean Arctic sea ice for the years 1989-93 on 21 December, the sea ice concentration on 21 December 2016 and the difference between the two data sets. Blue shades imply more sea ice and reds imply decreased sea ice compared with the mean. The original data come from the DMSP SMMI data set at the NSIDC.

The ice edges have retreated compared with 1989 - but as I wrote about in Record Low Arctic Sea Ice Extent we still have the very low sea ice concentration in the Barents Sea. There is also  still a very low concentration region north of the Bering Strait but the the Chukchi Sea and Hudson Bay have mostly frozen over.

...continue reading

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I was asked “what is an easy way to get a satellite image into Google Earth?”. Once I explained how I do it I thought it may be of interest to others. NASA have provided a really excellent web interface to some of their visual data called Worldview.

The Worldview description puts into perspective how good it is.

The Worldview tool from NASA's EOSDIS provides the capability to interactively browse global, full-resolution satellite imagery and then download the underlying data. Most of the 200+ available products are updated within three hours of observation, essentially showing the entire Earth as it looks "right now"

More than 200 data products within three hours…

Open worldview and this is the screen you are greeted with. It is easy to use. The key regions are the projection / copy / link tool in the yellow square on the right, the date control in the yellow box on the bottom of the browser screen and the layers control in the yellow box on the left.

Worldview opening screen.
Worldview opening screen.

I do recommend following the tour to find your way around the data sets.

Worldview tour screen
Worldview tour screen

If you click the layers button (red on the left) this is just a part of the choice of real time data you can easily access.

Some of the data choices available in WorldView
Some of the data choices available in Worldview

So you select the data you want to see, and then you can zoom in and easily download areas of interest. For some reason I always seem to find my way at this view

Worldview Antarctic stereographic view.
Worldview Antarctic stereographic view.

This movie I made shows how you can get  imagery from Worldview easily into Google Earth.

I hope you find this useful. It's easy to spend a lot of time looking at this data.

Navigation charts in Antarctica may not be as good as you think. It makes sailing in those regions a little more exciting than you could hope. Here is an example.

The coastline of Rothschild Island just to the west of Alexander Island, Antarctica. The navigation chart says the coastline location could be 5 miles in error
The coastline of Rothschild Island just to the west of Alexander Island, Antarctica. The navigation chart says the coastline location could be 5 miles in error

Five miles wrong... What does that mean?

Here is London with a 5 mile radius circle drawn on it.

London with a 5 mile circle drawn on it
London with a 5 mile circle drawn on it.

If you sailed your ship to a position - say the edge of Rothschild Island, you would not know the exact location of that coast to within the radius of that circle.

Just get your head around that. In this age of satellites, in 2016 we don't know the location of coastline of Antarctica to the same level of accuracy that we already know the topography of Mars, Venus and our Moon.

Why are they so bad?

As usual there are lots of reasons. Most of the coastlines were mapped out by people on sailing ships and huskie drawn sledges decades before the satellites were launched. That means the outlines of the coasts and water depths tend to be excellent. But absolute position - basically the origin of the co-ordinate system - can be out.

The bottom line is if you are trying to calculate position with a sextant and clock, it's hard enough in good conditions (for me!). But in a snowstorm when it has been overcast for several days? The historical navigators are my heroes.

In practice today does this lack of accuracy matter?

Charcot Island. A photograph of a repeater of the navigation display of RRS James Clark Ross in 2008.
Charcot Island. A photograph of a repeater of the navigation display of RRS James Clark Ross in 2008.

That picture of the ship's track tells the story. The ship has skirted the coast of the island, but according to the chart we ended up on land! I have a few examples like this from Antarctica. And even the mighty Google Earth has Charcot Island wrong.

A screengrab of Charcot Island from Google Earth Pro 20 Nov 2016. The island is displaced by ~11 nautical miles.
A screengrab of Charcot Island from Google Earth Pro 20 Nov 2016. The island is displaced by ~11 nautical miles.

Polar ship Captains, officers and crews take ships into areas that are genuinely unexplored. We don't know the coastline or the water depths well.

In fact, in Antarctica all you really can be certain of is you know you are going to be surrounded by icebergs and sea ice.

It's a big responsibility.

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The sea Ice is too heavy for the RRS James Clark Ross to make Rothera base right now. You may have thought the sea ice on the satellite images didn't look too bad, but it's all about how thick the sea ice is, and where the open water is.

To quote the radio officer Mike Gloistein:

The sea-ice around the bottom of Adelaide Island has been heavy and whilst (for those of you who look at the satellite pictures) there are some leads and areas of open water,  they are close to land and if we took that route (which also includes shallow water and rocks) and the weather then pushed the ice inland,  the ship could easily become stuck between a rock and a hard place.

And then the ship could get seriously stuck just like I said the John Biscoe did in my previous post. In that case the ship was rescued by Polarstern.

This was the satellite image I posted yesterday:

The MODIS satellite image off Adelaide Island 25 Nov 2016, with the location of the RRS James Clark Ross 0000 28 November 2016.
The MODIS satellite image off Adelaide Island 25 Nov 2016, with the location of the RRS James Clark Ross 0000 28 November 2016.

And this is a navigation chart of that region.

Section of the Navigation Chart around the southern tip of Adelaide Island.
Section of the Navigation Chart around the southern tip of Adelaide Island.

The light blue shading is shallow water and it's not a great place for a ship to go without freedom of navigation. The sea ice takes away that freedom. This is of course a very sensible choice by the ships Master, and exactly the same thing happened to a voyage I was on in 2004.

In another few weeks it will be clear for them.

I don't think this was predictable. You really have to be on the ground to see what the conditions are to make a call on whether it is safe or not. Two months ago on the 6 October I blogged about the sea ice and the potential of this happening, and said:

There are a lot of Antarctic research stations on the west of the Antarctic Peninsula, including Rothera, the largest British Base.  If the winds maintain the westerly direction then I can imagine it could be slow to resupply the base this season. There is time for it to change. According to the published schedule the ship is not due to arrive until 27 November 2016.

A slow resupply is not uncommon and I have been on at least one unsuccessful resupply voyage in my career. I took the picture below on 11 December 2004 under similar conditions.

James Clark Ross making very slow progress in compressed sea ice in Marguerite Bay, the Western Antarctic Peninsula.
James Clark Ross making very slow progress in compressed sea ice in Marguerite Bay, the Western Antarctic Peninsula.

Although it is not predictable, the fantastic British Antarctic Survey Operations will have planned for the consequences.

For a last point on the left of the navigational chart is one of my favourite place names:

Fullastern Rock to the west of Adelaide Island
Fullastern Rock to the west of Adelaide Island

As it says on the UK Antarctic Place Names website:

Fullastern Rock (67° 36′ 58″ S, 69° 25′ 59″ W) is a submerged rock on the west side of Johnston Passage, to the west of Adelaide Island. It was first charted by a Royal Navy Hydrographic Survey Unit from RRS John Biscoe in 1963.  The ship was compelled to go full astern to avoid this hazard  – a story succinctly captured by this evocative name!