This week at Macquarie Island: 7 October 2016
An update from the northern giant petrel census, the purpose of the Dobson spectrophotometer revealed, more Macca makeovers and our field hut tour moves to Green Gorge.
Northern giant petrel census
Over the past three weeks, the Tasmanian Parks and Wildlife team of ranger Chris and wildlife ranger Marcus along with field biologist Kim and the assistance of trusty volunteers (Ali and George–BOM, chef Rocket and carpenter Joe), have been searching the featherbed for breeding northern giant petrels. This work is part of the long-term monitoring of giant petrels on Macquarie Island to determine the population trend of these species informing international conservation management.
Northern giant petrels are one of two giant petrel species that breed on Macquarie Island annually, the other being the southern giant petrel. Northern giant petrels are listed as a rare and vulnerable species under state and federal legislation, respectively. Historically, the population has suffered from incidental mortality in fisheries and also predation by pest species, such as rats and mice. The coastal nesting locations of giant petrels also leave them vulnerable to inundation by storm events and large waves: in October 2015 their population was impacted when many nests were washed away by large waves.
As both a scavenger and a predator that consumes small fish and the remains of carcasses, the giant petrels play a vital role in the Macquarie Island ecosystem. Because of this, they were one species impacted during the Macquarie Island Pest Eradication Project (MIPEP), where in small numbers the giant petrels suffered incidental mortality through consumption of poisoned rabbit carcasses. The census aims to monitor population recovery post MIPEP and meet Australia’s international obligations for monitoring threatened species.
The census, conducted in the north west of the island, counts and maps all the northern giant petrel nests in a set area each year. This provides a comparable number of breeding attempts annually. A follow-up census in January counts all the surviving chicks, which provides an indication of breeding success. Last year the census showed that the population is stable and has continued to increase post-MIPEP. This year it appears there is a slight increase in breeding numbers, however only time will tell if the chicks survive to continue the cycle.
Penguins are footy supporters too!
Grand final weekend and unfortunately no chance of a live viewing of the finals here, however we managed to radio stream the AFL and Ali surprised us all with her troupe of footy penguins: one for everyone in their team colours, all excellently set off on the bright green of the newly-felted pool table!
Macca makeovers - signage part 2
We're continuing to spruce the old place up for summer and make it look as good as possible for our incoming expeditioners.
Rocket's been busy repainting the Macquarie Island sign on the distro hut by the front gate that was badly faded, and Ben has made the fuel farm look like new! Stay tuned on that site, still more to come…
Ozone and the Dobson
Part of the role of weather observers on Macca is to perform ozone measurements in two ways: a weekly ozonesonde balloon flight provides an ozone profile through the atmosphere, and hourly total ozone readings are taken through each day (when it isn’t raining) using a Dobson spectrophotometer, the star of today’s article.
Dobson ozone measurements at Macca began in 1957, and have been taking place almost continuously since. The length of the data record combined with the island's unique location which allows measurements of both antarctic and mid-latitude ozone levels make the ozone program here exceptionally useful for the global ozone monitoring program.
As well as providing protection from UV radiation the ozone layer is a major factor in controlling the temperature of the stratosphere, which can affect development of weather systems at the surface.
The Dobson is a beautifully solid instrument invented in the 1920s by a British meteorologist named (wait for it…) Dobson. It was the first instrument made to measure atmospheric ozone, and the “Dobson unit” (DU) is now the standard unit for all ozone layer measurements.
The instrument currently in use here at Macca, serial number six, was ordered in March 1936.
The Dobson works by comparing the brightness of two similar wavelengths of UV light from the sun, one of which is absorbed by ozone, and the other that isn’t. Two sets of these wavelength pairs, selected by moving a pair of mirrors, are used in each observation to improve the accuracy which can be affected by any pollutants in the air.
Incoming light is split into the required wavelengths using a system of quartz prisms and mirrors, and then an “optical wedge” is used to dim the brighter, unabsorbed wavelength until it is the same brightness as the ozone absorbed light. The amount of dimming required by the optical wedge tells us how much ozone is present.
A periscope–like sun director can be aimed at the sun to direct light into the instrument, or when the sun is unavailable (this is Macca after all) the sun director is removed and light from the sky directly above the instrument is used to take a Zenith reading.
To take a reading, the operator first adjusts the angles of the mirrors according to the current instrument temperature to compensate for temperature effects on the prism, and then moves the optical wedge by means of a dial until a micro-ammeter indicates the brightnesses are matched. The position of the wedge and the precise time of the reading are used to calculate the total amount of ozone above the instrument. Two sets of three to five readings (depending on type of reading and cloud cover) are taken per observation. Given suitable conditions up to eight observations are taken per day.
Despite satellites providing global ozone data since the 1970s ground based measurements remain important by providing consistent long term records, and for calibrating the satellite data. Dobson instruments were crucial in discovering the presence of the Antarctic ozone hole in 1984.
Thanks to the bureau ozone guru Matt Tully for his help getting info for this article.
Moving on around the island on our tour of the field huts, we come to Green Gorge, approx. halfway down the island on the east coast. A chalet–looking wooden hut, its installation wasn't nearly as dramatic as Brothers Point hut, but it is probably the most popular hut on the island for expeditioners looking for time away from station due to its comforts and location.
With the commencement of the aurora observation programme at Hurd Point in the 1950s, it became important to have a stopover point on the island so people didn’t have to travel back and forth in one hit. A low cave at the top of the beach at Green Gorge was the original sleepover spot, with the first hut being constructed in December 1954 to provide some improvement on home comforts.
Station Log 28/4/54
Whilst on the subject of huts, this seems an opportune time to mention the need for a hut at Green Gorge if it is intended that two or three men may be permanently stationed at Hurd Point. On the return trip from Hurd Point I had an injured leg, and it was not a very enjoyable experience to have to drag myself to Sandy Bay with the alternative of spending a very uncomfortable night on the plateau.
Green Gorge hut by Louise Crossley
The hut, soon dubbed “Shangri–La” (not the food store) was delivered to the site on 29 December 1954 by DUKW from the supply ship Kista Dan and erected that day by a party of ten 1954 & 1955 expeditioners – not a bad effort, considering they were back on station for the changeover party by 7 pm – though it still ‘had to be painted and fitted inside yet’.
The original Shangri–La was set up with two bunks and one window and was considered the most luxurious hut on the island. Improvements were regularly made and the hut was well–maintained.
Green Gorge Hut log 12/4/67 – Ray Gully & Peter Ormay
Warm hut and nice fluffy blankets make a welcome change after staying in the unheated huts of HP and CC which have a total of 8 gals of kero left between them to last the year… A public flogging would not be punishment enough for anybody who suggest that the pastel blankets are “too good for field huts”.
However by 1976 it was decided a new, larger hut was needed and one was delivered by LARC in November of that year. Construction didn’t start until the second half of the following year.
Green Gorge Hut log 24/8/77 – Rod R
Began setting up housekeeping for a long stay to erect new hut.
Green Gorge Hut log 30/9/77 – Keith Blundell
By knockoff time Rodg had excavated an area suitable for the tank and we had almost completely filled in the terrace. You beaut.
Green Gorge Hut log 17/10/77 – Keith Blundell
After lunch there is no wind started fixing the roof. A layer of Forteceon then silver sided insulation and then the corrugated iron by knock off time all the roof covered down and screwed and the end fascias fixed.
Green Gorge Hut log 16/11/77 – Nigel Brothers
1977 crew have done a superb job of the new ski lodge. It’s hard to appreciate the amount of work gone into the job unless one saw the site etc beforehand. As Mick Brown said – all is needs on the sun deck is a barbecue.
The original hut was retained as the food store, whilst the new hut was renovated in May 1989 with the addition of a new window and again in 1995 to add a new veranda and kitchen window. Currently the hut sleeps five in comfort, has a delightful picture window known as the ‘TV’ and plentiful king penguins and elephant seals as neighbours. Best of all, it doesn’t require a ‘jump down’ or ‘jump up’ to access, although there is some bog to navigate – it's Macca after all!
Green Gorge Hut log 26/11/97 – Karen Evans
I can’t believe it. Where else can you sit on the beach and watch orcas swim by, have seals on your right, penguins on your left, gulls, albatrosses and petrels flying above you, the most amazing coastline unfolding on either side and slopes of the most wonderful botanic patterns in lines of brown and greens behind you?