Historic Shift in Wind Patterns Over Bay Blows Away Water Quality

As the sun set over Annapolis harbor on a recent evening, eighty sailboats, with golden and white sails, slashed back and forth, jostling for position behind a motorboat with a man holding a starting gun.

From the days of privateers to the Wednesday night yacht races in Annapolis harbor, the Chesapeake’s winds have long played an outsize role in the region’s economy and culture.

But some scientists have recently discovered that those wind patterns have undergone an historic shift.  And this change in average wind direction has had an impact not only on sailing, but also – surprisingly enough – on water quality in the Bay. This connection was reported first in the Bay Journal by Karl Blankenship. 

Until about 30 years ago, the prevailing winds that blew across the Bay in the summertime came mostly from the south, explained Dr. Michael Kemp, a professor at the University of Maryland Center for Environmental Science, during an interview with Bay Daily.

These southerly winds would sweep the 200 mile length of the Bay.  Winds that run in this direction are unobstructed by trees or land masses, which allows them to build up speed, make waves, and stir up the Bay’s waters.

But then this mixing machine broke down.

 “Starting probably in the mid 1980’s to the present, we’ve seen the winds moving around primarily from the westerly direction – that is, out of the west,” Dr. Kemp said. “We still get southerly winds. But we get much higher frequency of winds out of the west, which has a very different impact -– in fact, much less impact on the circulation of the Chesapeake Bay.”

The Bay is narrow from west to east-- only five miles across near Annapolis. So winds from the west do not have much room to make waves and stir the high-oxygen surface water into the oxygen poor depths. This reduced circulation of oxygen makes it harder for oysters, clams, worms and other critters on the bottom to survive.

Low-oxygen “dead zones” are caused by water pollution – nitrogen and phosphorus from sewage plants, farms, lawns and other sources. But the right kinds of winds and currents can help breathe life back into suffocating waters.

Dr. Malcolm Scully, an oceanographer at Old Dominion University, wrote about the subject in an article in the Journal of Physical Oceanography.

 “The extent and severity of these dead zones appears to be very sensitive to what the wind climate is like,” Dr. Scully said in an interview. “So when we have summers in which the winds are blowing predominantly out of the west, as opposed to the south, it seems like the water quality is much, much worse in those years. And that’s going to have an obvious impact on the biological organisms that live in the Bay.”

Dr. Scully said that the fact that winds affect water quality doesn’t mean that we shouldn’t care about pollution.  Just the opposite, in fact.  It means we have to be even more diligent about reducing pollution – because that’s the one factor we can control.  Rain also affects water quality in the Bay, and people can’t control that, either.

Dr. Scully added that his findings might help answer a vexing question about the Bay: why billions of dollars spent reducing nitrogen pollution have had a sometimes erratic impact on the dead zones. The answer is blowing in the wind.

The shifting wind patterns appears to be caused by a giant El-Nino-like weather pattern over the Atlantic Ocean. High and low pressure areas in the so-called North Atlantic Oscillation move around every 30 years or so. Recently, there have been signs that this pattern may be shifting back again, according to Dr. Scully and other scientists. A signficant change could be in the wind, perhaps even this summer.

Of course, predicting the wind is as tricky as forecasting the weather.  But, if Dr. Scully is right, and this North Atlantic system is about to flip back, that could mean a return of more powerful southerly winds to the Chesapeake Bay.  That could mean better water circulation and a retreat of the dead zones.

And that would be good news not only for oysters dying to breathe, but also for sailors looking for a good run north.

 

Article and photos by Tom Pelton

Comments

[Donna L. West]

I remember when Mike first came to Horn Point, back in the late 70's, it seems like only yesterday. Wonder how these changing wind patterns will affect the annual Governor's cup sail boat race held annually in August, from Annapolis to St. Mary's College of Maryland?

Donna L. West
SMC Class of 1976

[Tom Pelton]

A great question, Donna. I imagine that the sailors can adjust their courses to the changing wind directions. (As long as their is strong enough wind of some kind). The main question, I believe, is how choppy the waters will be, with more southerly winds generally meaning bigger waves.

[Tom Price]

Do you think the greater number of boats now, over the number 30 years ago, continually churning the surface has any beneficial effect in aerating the water?
I have to say that I have had the impression of fewer strong Southerlies from when I first started racing on the Bay in the late 1960s. Long Island Sound sailors say the same thing. Their body of water is more east west oriented.
The winds that are from the el Nino are the weather system winds, while so much of our local wind is caused by thermal development (rising air from land heating, drawing in cooler air from the cooler Bay water. You would think that increased paved surfaces causing hotter conditions on land would enhance the thermal breeze?
There is no worse summer wind than those hot, shifty, puffy Westerlies blowing from the heated land, bringing their raw heat (and flies) over the Bay!