After Pliny’s monstrosity, many centuries went by before this question was really tackled again.  In 1815, Edward Forbes took a ride aboard the HMS Beacon, where he dredged the bottom at depths from 1-1,380 feet (0 – 420 m).  Just so you know, the average depth of the ocean is about 12,000 feet (4,000 m).  So, when I say he was barely scratching the surface, I’m not really exaggerating.  But nevertheless, he dredged the depths that he did and found that the deeper he dredged at, the less things he found.  So naturally, he thought, there must be a “zero point” at which no animals live.  He wildly extrapolated his data and determined that below 1,800 feet (600 m) there exist no animals, and he called this the “azoic zone.” So, Forbes’ answer to how many species in the deep sea was a big fat “not many.”

Luckily this “azoic zone” nonsense only lasted about 50 years.  In 1869, Charles Wyville Thomson and the rest of the crew onboard the HMS Porcupine pulled up animals from 14,610 feet (4,450 m) deep in the waters south of Ireland.  These results were later confirmed by the Challenger expedition which found animals at all depths, all over the globe.  This undeniably proved there was life at all depth of the oceans- but the question still remained.  How many species in the deep sea?

Fast forward to 1992.  Frederick Grassle and Nancy Maciolek conduct a massive (for the time) survey of the tiny animals that live in the sediments in the deep sea.  These are not the cute crawlies that live on top of the mud that had been previously sampled with dredges.  These are the small animals that live their lives between the grains of dirt at the bottom of the ocean.  Of the 798 species that they found, over half were new to science!  Pliny’s head would explode if he heard that more than double the total animals he thought existed in the whole ocean were found just in the mud.

Grassle and Maciolek did some impressive math and ended up calculating that they were finding one new species per square kilometer they sampled.  Let’s break that down.  One square kilometer is equal to a little more than one-third of a square mile.  So, they are basically finding three new species in each one-mile-square block of mud they are sampling.  This means if they were to sample an area the size of New York City, they would find around 782 new species, and if they were to sample an area the size of London, they would find about 1,572 new species.  These new species add up fast – you see, there are 300,000,000 square kilometers (115,830,647 square miles – almost 30 Europes or 431 Texases) of mud deeper than 1000 m in the ocean. The end result of all this is a conclusion of 300,000,000 species living in the mud at the bottom of the deep ocean.  This is not counting swimming things!  That’s a heck of a larger estimate than the 176 species estimate of centuries ago.

.It turns out that this calculation of Grassle and Maciolek was probably a bit of an overestimation.  They realized that much of the ocean is oligotrophic, or not very nutrient-rich and therefore not very productive.  This would mean that in many areas of the ocean, the rate of new species added per square kilometer is probably much less than what they found in their sampling area.   So, they ended up conservatively estimating the true number at more like 10,000,000 species in the mud. This is still a huge amount of diversity in the deep sea.

Grassle and Maciolek’s 10 million species hypothesis sparked quite the controversy, with biologists from many sub-disciplines quickly arguing for or against the high number.  Isopod biologists Poore and Wilson said they had seen even more diversity just among isopods in their samples than the average number of species per 100 samples that Grassle and Maciolek had used in their calculations.  This, they argued, must mean there are even more than 10 million species!  In 1971, though, Thorson argued that there were only 160,000 species in the oceans across all depths- so far less than 10 million could be in the deep sea.  In 1992, May argued that only 500,000 species would be possible in the deep sea.  Lambshead in 1993 reminded everyone that there are a boatload of nematode worms and other animals (collectively called meiofauna) that live in the mud that were too small to be sampled by the gear Grassle and Maciolek used.  This, Lambshead argued, could mean a total of 100,000,000 marine species.  Consensus just could not be reached.

Here’s the problem, though.  It is a hard question to answer.  Each person who has attempted to answer this question was doing the best with the data that they had at the time (except Pliny- that guy was just an idiot okay). However, species diversity and especially how many species you discover in each new deep-sea “block” can vary considerably at different depths, regions, and oceans. Grassle and Maciolek’s encoutering 3 new species per block was based on data from the North Atlantic. Does 3 new species “rule” also apply to other parts of the Atlantic or to the Pacific? So without massive amounts of data, it is likely we will be kept guessing for a few more years to come. So, I can’t tell you exactly how many species are in the deep sea, but I can tell you that we currently have 409,543 named species in the ocean (World Register of Marine Species, accessed 03/18/2019).  The best part is that we are getting better and better at discovering new species, and hopefully in years to come we will be much better equipped to answer this question realistically.

Cover photo credit to Monterey Bay Aquarium Research Institute (MBARI).

The post How many species are in the deep sea? first appeared on Deep Sea News.

So please, sit back and appreciate the awesomeness of sea science while watching the gorgeous, sinuous streams of our ocean’s currents.

The post Feel the zen of the ocean with this coastal current map first appeared on Deep Sea News.

What do you think of when see the term “seawater”? Salty water? Perhaps fish-poo-covered-bacterial-ooze-slime-haven-so-salty-I-puke-in-my-snorkel-every-time-it-touches-my-tongue? Well, the definition of seawater has been limited by how we can measure it and what type of information that we wish to glean from knowing something about seawater.

For over 30 years now, researchers have defined seawater based solely upon its salinity. The problem is that salinity is measured by conductivity and this measurement assumes that the entire world’s oceans have the same salinity. It is well-known now that this is not true. For instance, deep sea water is more dense because it is colder and concentrated with more salt. In fact, this slight difference between deep sea water and surface water explains different behaviors of each body of water. Oceanographers can actually track the movement of water in ocean by mapping the changes in salinity over time for a body of water.

Over the course of the last few years. Dr. Frank Millero and colleague have created a new definition of seawater that takes into account the many advances in ocean thermodynamics over the last 30 years. If you are interested in the details of the new equations and more of the history you can check out this freely downloadable report (link opens a pdf) from the Australian environmental agency CSIRO. The interesting parts are summarized in this press release from CSIRO:

Salinity, comprising the salts washed from rocks, is measured using the conductivity of seawater – a technique which assumes that the composition of salt in seawater is the same in all the world’s oceans.

“The new approach, involving Absolute Salinity, takes into account the changes in the composition of seasalt between different ocean basins which, while small, are a factor of about 10 larger than the accuracy with which scientists can measure salinity at sea,” Dr McDougall says.

Until the new description of seawater is widely adopted, ocean models will continue to assume that the heat content of seawater is proportional to a particular temperature variable called “potential temperature”.

“The new description allows scientists to calculate the errors involved by using this approximation while also presenting a much more accurate measure of the heat content of seawater, namely Conservative Temperature,” Dr McDougall says.

“The difference is mostly less than 1ºC at the sea surface, but it is important to correct for these biases in ocean models.”

This will be an important correction for climate change change models. Even though we here at DSN think the deep sea is the most important habitat on the planet, much of the economical parts of the ocean (i.e. fishing industries, coral reef tourism, etc.) lie in surface waters which are more sensitive to smaller fluctuations in temperature. By taking into account heat capacity and potential temperature, climate change models will be better tweaked and will reflect a more accurate model of ocean processes into the larger picture.

Hat tip to Wild Shores of Singapore.

The post Seawater Redefined first appeared on Deep Sea News.

Of all the planets in our solar system, ours alone is covered in a life-giving, liquid blanket of blue. It is out of these depths that Abyss, Proctor & Gamble’s biggest fashion trend predicted for 2009/10 emerges.  Abyss is an immersive experience that celebrates water as the new gold, and a sense of preciousness that is heightened by scarcity. It is mysterious, enigmatic and attractive. Abyss invites exploration and rewards it with rare treasures from the deep. You’ll recognise it in wet textures and finishes, in sensual undulations that soothe the eye and phosphorescent glints that catch it.

That’s right the fashion rage is called Abyss and it has already hit the runway. Calvin Klein released the Urban Mermaid collection this spring.  No I didn’t make this up.  So how can you make sure you doing it right?

• With your makeup, “Don’t be afraid of colour”
• “Keep blues translucent and focus on one element,” remember “The key to applying the intense colours of Abyss without looking garish is to go for translucency.”
• Minimal black that is blended and refined
• Let the shine sell the make-up
• For hair, “looser, more casual looks with a light touch” and try a look such as “Fresh Hair, Deep Texture and Tumbling Cascades.”

Of course all of this is old news for us here, we been doing this for years.  DSN fashionable before it was fashionable.

The post Deep-Sea News, Now More Fashionable Than Ever first appeared on Deep Sea News.