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THEY say, where there鈥檚 muck, there鈥檚 brass. Anyone who has stumbled upon ambergris will confirm this. The weathered whale excrement is extremely rare, but it can be found on beaches in many parts of the world. It is unprepossessing: dusty grey or brown with the faintest whiff of earth and sea, mixed with something unfathomably animal. Yet this stuff is so prized by perfume-makers that a lump the size of a human head could fetch you 拢50,000 or more.

Traditionally used to boost the staying power of scents, these days a synthetic alternative means that ambergris is found only in . But now scientists have discovered that it harbours another treasure. Adrift in the oceans for decades, even centuries, before washing ashore, each lump is a message in a bottle from a long-departed whale. It holds clues about the lives of these animals before whalers came to plunder them. 鈥淭here鈥檚 really quite exciting potential to look at the impact of whaling on whale health and diversity,鈥� says .

Ambergris also contains historical information about the oceans, especially the marine species foraged by the whales that produce it. It could even give insights into how these animals might respond to the challenges they face as a result of climate change.

Ambergris usually makes landfall after a long voyage, originating as black, waxy lumps in a sperm whale鈥檚 colon. Nobody knows exactly why it forms. It may encase the sharp beaks of the squid that the whales prey on to stop them damaging the gut, or it may simply be a quirk of metabolism. The fresh stuff, reeking of faeces, has much less value than ambergris matured by a long soak in the sea. This latter form, known as jetsam ambergris, is composed chiefly of ambrein, an organic chemical capable of stabilising volatile scents, which is what made ambergris so sought-after by perfumiers. But it is ambrein鈥檚 ability to repel water and resist decay that first drew the attention of Macleod and his Cambridge colleague . They realised that ambergris could encase DNA and protect it from the elements. What鈥檚 more, it could do this for centuries: in 2019, a team led by chemist , UK, .

Sperm-whale speciality

In a preliminary study, Macleod and his colleagues succeeded in sequencing stretches of DNA from Rowland鈥檚 ambergris collection. This confirmed what many had suspected but never been able to show, namely that . Now, the researchers want to sequence the DNA in ambergris more thoroughly, to read the history hidden in the whales鈥� genomes. Studies of ancient DNA from other marine mammals show this approach can paint a . For example, in 2019, team member , Denmark, and his colleagues combined analyses of DNA from walrus bones with historical and archaeological information to . This revealed the existence of a genetically unique population that appears to have been hunted to oblivion by Norse settlers during the 11th and 12th centuries. 鈥淲hat really surprised me is how far back in time humans have had an impact on marine ecosystems,鈥� says Tange Olsen.

In the 20th century, commercial whalers slaughtered at least 3 million whales. Studies of ambergris DNA could help researchers assess the relative sizes of pre-whaling sperm whale populations and their genetic diversity. Comparison of ancient whale DNA with modern samples might also hint at how natural selection has shaped these animals.

But ambergris doesn鈥檛 just contain DNA from sperm whales. Macleod and his colleagues found patchy sequences from a multitude of other organisms, too, ranging from bacteria and other microbes to intestinal worms and armhook squid, the whales鈥� usual prey. Exploring the microbial sequences in more detail could allow researchers to get a handle on the gut microbiomes of past sperm whale populations, which in turn could reveal how the pressure of whaling affected their foraging strategies and microbiome diversity, says Macleod. Sequences from the worms and squid could reveal knock-on effects on prey animals. 鈥淚t shows the kind of ecological ripples resulting from killing lots and lots of whales on all these other species,鈥� he says.

Studying whale digestion and the role of their gut microbiomes can even help us understand our planet鈥檚 biogeochemistry and climate. 鈥淲hales are consuming a large amount of carbon every day,鈥� says . She and her colleagues have been working with Indigenous Alaskan subsistence hunters to see how microbes in the guts of bowhead whales influence the , a carbon-rich chemical found in species the whales eat. Others have shown that whale excrement , such as nitrogen, in the water column, nurturing the growth of plankton that consume carbon as they photosynthesise. As well as storing carbon in their bodies while living, whales often take it with them in death, sinking to the deep ocean where their .

Understanding more about whale gut microbiomes will also help scientists keep track of how modern populations are coping with climate change and other stresses. 鈥淭he microbiome might be a really useful metric for health in these animals,鈥� says Apprill. Ambergris would provide 鈥渁n amazing baseline鈥� to better understand and add context to data from today鈥檚 animals, she adds.

Sadly, we are unlikely to see a return of the pristine oceans of the pre-whaling era. But ambergris could help us understand how these charismatic beasts might survive a future in the noisy, warming world we have created. For that reason, at least, it would be priceless.