On December 21st 1872, 150 years ago this month, HMS Challenger set off from Portsmouth, UK for a four year voyage around the world. She was heavily modified from her former role as a small warship into a floating laboratory to scientifically explore the oceans. With a small complement of scientists in addition to her crew the Challenger travelled almost 69 000 nautical miles between 1872-76. I've owned one diatom strew slide by Klaus Kemp for some years but the anniversary prompted me to search for a second on eBay. Some Challenger samples were widely distributed amongst slide preparers past and present so slides are not uncommon. It can be pot luck on pricing as secured a second diatom strew for ca. £16 made by Suter but a few days later a well labelled Challenger sample of Globigerina ooze fetched £96 (see below).

Diatom strew slides can have a particular appeal if they can be directly associated with a far flung place on the globe that will never visit. The association with a specific survey investigation adds an extra appeal as prompts exploring resources describing the expedition. A 47 form arranged diatom slide of a sample taken during the Scottish National Antarctic Expedition led by W S Bruce has already been shared in the March 2020 issue of Micscape, it was prepared by Klaus Kemp.

The website www.19thcenturyscience.org has a wealth of resources on the expedition including a page listing the charts of the sounding areas.

The biodiversitylibrary.org website hosts copies of the Challenger Reports and Zoology. Volume IX, 1884 lists the 'Observing Stations'. The station entries for the two slides owned are shown below. The archive.org site has copies of all the reports spanning fifty volumes but the indexing makes it tricky to seek out a volume required.

Preparer Klaus D Kemp. 'Royal Sound Kerguelen Island, 28 Fathoms, Challenger 149D'. Preparer's sample code 788R, Pleurax mount dated 7/2002.

Klaus Kemp was a highly respected preparer of arranged diatom slides as well as striking exhibition slides. He is very much missed after his sad passing earlier this year. The Challenger slides are of particular interest and scientific value if properly labeled with the location and depth at which the sample was taken as this allows the station to be found in the published reports. In this example of a fully labelled slide the station 149D is also given allowing the exact spot to be found on the published charts.

Kerguelen Island, station '149 d' is marked.

Station 149 D entry. Crop of chart and station entry courtesy of the biodiversitylibrary.org website.

I only possess a limited number of named location marine deposits from the late 19th century onwards but if typical they can be of limited value to the non-expert in diatom study like myself. The appeal more remains in the history and location of the sample—in this case owning a tiny fragment of the Challenger expedition! The work up of the deposit retains all siliceous material so sponge spicules can be quite dominant. Centric diatoms can be the main species and although the smaller species survive intact, invariably the larger ones (and for me easier to ID to at least genus) do not. For these sort of slides it can be useful to draw a map at low mags to plot the more interesting diatoms so they can be found more readily at higher mags.

This station 149 D example illustrates this. Linear sponge spicules are dominant and the larger centric diatoms are fragments. Images of the selected whole diatoms found are shown below.

Challenger station 149 D, Zeiss 6.3X, darkfield. Sponge spicules dominate, centric diatoms are the commonest species
which survive when small but fragments when larger. Few pennate diatoms were found.

Zeiss 25X slight oblique, ca. five image stacks with CombineZP. Left, one of the couple of pennates, and right, the sole square diatom seen in the sample.

Preparer Richard Suter, 10 Highweek Road, Tottenham [London] 'HMS Challenger Diatomaceae, Atlantic, 1990 Fathoms

Richard Suter (1864-1955) was a well regarded preparer of mounted slides working from the address on the label (see Brian Stevenson's bio' on Suter on his splendid Historical Makers of Microscopes and Microscope Slides website). Some detective work is required to determine the exact location of this sample but coincidentally when buying this slide another Challenger slide was for sale on eBay that may provide a clue. Labelled 'Globigerina ooze, "Challenger", Station 338, 21st March 1875, Atlantic Ocean 1990 fathoms'. All the 300+ sampling stations are listed in the Discovery Reports, so a text search showed that only one station took samples at this depth suggesting a deposit from the same sampling location. The deposit is noted to be a Globigerina ooze in the station commentary. Although a calcareous deposit, siliceous organisms such as diatoms and radiolaria were also reported from other such oozes in significant amounts. Station 338 was in the middle of the South Atlantic SE of St. Helena. The tiny island west of the sounding station labeled 'Trinidad' is the Trindade and Martim Vaz archipelago.

Station 338 details believed to be the same station as the Suter slide sample as the only station recorded sampling at 1990 fathoms.
Crop of chart and station entry courtesy of the biodiversitylibrary.org website.

The Suter slide is a more interesting sounding for study, as shown below with comments in the captions. Showing my ignorance of marine diatom ecology is there any particular reason why in the two soundings illustrated and if typical of the Atlantic deposits, centric species seem by far the more dominant over pennate?

Suter 1990 fathoms, suspected to be Challenger station 338, mid Atlantic, Zeiss 6.3X, darkfield. Sponge spicules are much less evident,
smaller centric diatoms are the commonest species. Few pennate diatoms were found.

Upper left. Zeiss 25X phase, one of the few larger diatoms that stayed essentially intact.
Upper right. Zeiss 16X phase, a variety of centric species seen but one or two dominate. A few pennate species present but less common as seen in lower half of image.
Lower left and lower right, Zeiss 40X phase.

 

Micscape invitation. In this 150th anniversary year of the beginning of HMS Challenger's voyage, if readers have examples of prepared slides from named soundings why not share them. It would be interesting to see how they vary. Do any readers have example slides of selected species from strews rather than, as above, a general strew of the deposit?

Comments to the author David Walker are welcomed.

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