Cruising World - June 2018

june/july 2018

cruisingworld.com

130

C

rossing the Gulf

Stream is a rite of pas-

sage for many East

Coast offshore sailors. I’ll nev-

er forget my fi rst time. The

Stream seems to generate its

own weather, and the precip-

itous clouds on the horizon

ahead were the initial clue that

we were approaching. Then

there was the sudden spike in

the temperature of the ocean,

up into the high 70s, as con-

fi rmed by the boat’s seawater

thermometer. The water it-

self shifted to a darker shade

of blue, fl ecked with yellow

patches of sargassum. And with

a slight northerly breeze (thank

God it was slight) leaning into

the northward fl owing current,

the waves stood up into a pro-

gression of steep but reason-

able, negotiable hills, the boat

rising and falling with their

fl ow. It was all very memorable.

The Gulf Stream, the so-called

“river in the sea” that trucks

along in places at a good 4 to 5

knots, is truly a force of nature.

And, remarkably, it is also

slowing down.

Such was the conclusion of a

pair of recent scientifi c studies

focused on the Atlantic merid-

ional overturning circulation

(AMOC) — an ocean circula-

tion system that includes the

Gulf Stream — recently pub-

lished in the journal Nature.

Simply put, a section of the

warm, salty surface waters of

the Stream eventually peel off

to form the North Atlantic

Current which ascends into the

high, chilled Nordic latitudes,

heating the atmosphere on

the way. There, the water cools

and the weight of its salinity

causes it to plunge into the

depths, where it begins a return

journey down the coasts of

North and South America. The

entire cycle has been likened

to an “ocean conveyer belt”

that plays a key role in Earth’s

climate by exchanging warm

water from the equator with

cold water from the Arctic.

And the conveyer belt, so

crucial to distributing heat

across the planet, is not as

quick as it used to be.

According to the Nature

report, the two studies that

issued this fi nding used vast-

ly different methodologies:

“classic examples of ‘top-down’

and ‘bottom-up’ approaches.”

The former based its report on

direct measurements of sea-

surface temperatures; the latter

relied on measuring deep-sea

sediment cores that refl ect the

speeds of the bottom waters on

their return fl ow of the AMOC

(stronger currents move thicker

grains of sand). But both de-

termined that the weakened

AMOC has declined in strength

by 15 percent, which the Wash-

ington Post reported as “a de-

crease of 3 million cubic meters

of water per second, the equiva-

lent of 15 Amazon Rivers.”

Mercy.

In science, as in life, one

thing leads to another. In this

case, perhaps ironically, the

rapidly melting glaciers of the

Greenland ice cap and the van-

ishing sea ice above the Arctic

Circle are playing a signifi cant

role in this equation. Yes, those

waters are cold, but they’re

also fresh, and fl oat atop the

surface; their mass infusion

into the briny sea disrupts the

formation of the dense water

that’s a key component in the

spinning AMOC.

So, what does that mean to

sailors and, you know, human

beings? Well, should the brakes

on the Atlantic circulation

continue to be pumped, among

other things, it could result in

drastic changes in European

weather, dramatic fl uctuations

in hurricane frequency and an

abrupt rise in sea levels on the

East Coast, with a backed-up

Gulf Stream having no pl ace

else to go. There are lots of oth-

er scenarios, and none of them

are great.

One of the central questions

of our time, of course, is the

degree to which man-made

sources have contributed to cli-

mate change, and in this case,

what role they played in the

AMOC slowdown. Interest-

ingly, the authors of one study

attribute the cause mainly to

human-induced factors (i.e.,

those that have played a part in

the relatively new phenomenon

of swiftly melting ice), while

those of the other suggest it

probably began for natural rea-

sons around 150 years ago but

has since been aided and abet-

ted by our own collective im-

pact on the changing climate.

As with contemporary poli-

tics, there is no clear consensus.

So, for now at least, we’ll

leave it to the noted oceanog-

rapher/poet Bob Dylan, who

once sang, “Come gather round

people; Wherever you roam;

And admit that the waters;

Around you have grown; And

accept it that soon; You’ll be

drenched to the bone.” For, yes,

the times they are a-changin’.

Herb McCormick is CW’s

executive editor.

The Gulf Stream, the so-called “river in the sea” that trucks along in places at a good 4 to 5

knots, is truly a force of nature. And, remarkably, it is also slowing down.

Composite imagery from several high-seas weather models

shows the path of the Gulf Stream up the U.S. East Coast.

DOWNED Stream

Off Wa tch

COURTESY OF THE OCEAN PREDICTION CENTER/NOAA