a mysterious portal has opened up off the coast of new york. its boundaries should be obvious even to landlubbers: the sea turns from murky green to a deep, clear blue, jumps a few degrees warmer, and unexpected tropical sea life begins to appear. it’s like a gateway into the caribbean, hundreds of miles north of where you’d expect it to be.
these strange areas are a regular feature of the waters off new york city, called warm-core rings: swirls of tropical water that break off from the gulf stream and head our way. for naturalists, they’re a way to see species that wouldn’t otherwise live so close to new york. but they also form part of a broader system that helps governs the climate and ecology of the north atlantic, but a system that’s changing with anthropogenic climate change.
we call that broader system the atlantic meridional overturning circulation (amoc). it’s a vast cycling of atlantic water that sends warm currents northeastward from the caribbean via the gulf stream, and cold water back southward along the eastern atlantic. the gulf stream part of that circulation is responsible for the almost-tropical weather of the southeastern united states and the uncharacteristically warm weather of northern europe, given the latitude.
the gulf stream turns east at cape hatteras in north carolina, so it doesn’t influence new york waters directly. instead, it generates these warm-core rings, clockwise-spinning eddies with gulf stream-like qualities that veer toward the continental shelf off of long island and new jersey. inside the ring is warm, highly saline, and nutrient-poor water, lending it a deep blue color unlike the murkier plankton-rich green waters of the continental shelf.
these warm-core rings are stopped by the steep cliffs at the edge of the continental shelf, but still have the potential to alter the seas closer to us. according to one paper, they bring distinct changes to microbial communities that alter how bacteria cycle nutrients into and out of the water. that, plus their high salinity, have ecosystem-tweaking properties.
the number of warm-core rings seems to be increasing as part of a broader set of ongoing changes to the amoc. as the polar ice caps melt from climate change, they release less-dense fresh water that doesn’t sink as easily. but north atlantic ocean water sinking is an important part of the current cycles, so the meltwater has the potential to slow or even stop the gulf stream (kinda like a clog in the pipe), leading to warmer water around our area.
the slowing gulf stream has the potential to bring stronger storms to new york city and drier weather in europe. and more salty water from warm-core rings could alter the habitability of our shelf water for important commercial fish species and other sea life. note that while there are definitely more warm-core rings, there haven’t been direct measurements of the gulf stream slowing yet.
for mariners willing to take a trip just beyond the shelf’s edge—around 100 miles south of long island—these warm-core rings provide an opportunity to spot sea life that might otherwise require a visit to the caribbean. the american princess runs near-monthly deep-sea trips from brooklyn during the warm months of the year. we usually spend more time in the productive hudson canyon that carves through the shelf, but the trip always starts by looking for eddies from warm-core rings in deep (6000+ foot) waters, aiming for tropical specialties.
the color change and temperature jump of the water is usually pretty obvious once you’ve entered the warm-core ring. you’ll also notice clumps of sargassum, a seaweed that’s abundant south of the gulf stream in a calm area of warm water called the sargasso sea. the most common bird is perhaps the band-rumped storm petrel, an enigmatic seabird whose regular presence near new york was only recently confirmed when these trips started targeting the rings. also common are audubon’s shearwaters, a small black-and-white tropical-breeding seabird associated with sargassum. scarcer but expected tropical birds are bridled terns plus black-capped petrels, endangered caribbean seabirds whose eerie calls have earned them the nickname “diablotín” or little devil.
in my opinion, it’s the non-birds that make these warm core rings feel tropical. flying fish are abundant, constantly zooming away from the disturbance of passing boats. you might spot portuguese man o’ wars, relatives of jellyfish that look like floating plastic bags with large purple streamers, which are composed of many smaller individual organisms. you might also find striped dolphins, beaked whales, sunfish, and sharks—this most recent time, we spotted a whale shark, the world’s largest species of fish. where the warm core ring’s water intrudes onto the shelf, you’ll continue to see some of these species as you travel back toward land.
a trip to florida might or might not sound easier to stomach than a 150 mile boat ride into the atlantic ocean. but for many nature likers, saying “i saw something in my home state” is a very important point of pride to keep track of. it’s often motivation enough for me to spend the night on a whalewatching boat just to see what kind of strays these warm-core rings have carried into new york waters.
postscript
it’s fall migration, the best time of year! sure, the birds are prettier during the spring migration. but during the fall, the number of birds is way higher on account of the juvenile birds. also, those juvenile birds are often migrating for the first time, and have a tendency to get lost—so the chance of finding something uncommon is a lot higher in the fall.
that being said, birds aren’t the only things migrating in the fall. no less spectacular is the insect migration. i probably saw a thousand or more green darner dragonflies hovering around a field in the park last week. and i’m really excited about this photo i got of a monarch getting ready to migrate south from breezy point, queens:
if you want to experience fall migration with me, i’ll be leading or attending a few events next month that you can come find me at.
on october 7th from 6am to 2pm, i’ll be at shirley chisholm state park (the skybowl on the fountain avenue side), helping to count birds at the big sit. registration is required, click here.
and because i love sitting so much, you’ll also find me at the feminist bird club x bird collective bird sit on october 14th from 9am to 1pm in prospect park, where they host smorgasburg. register here.
finally, i’ll probably write another post before then, but i’m leading a walk in prospect park on october 21 from 9am to 10:30am. meet at the stranahan monument at the park’s north entrance. registration not required but encouraged.