The advance of the tides over time has been documented by core samples, seismic data and sediment studies.
20,000 years ago
At the height of the last ice age, the Delaware Bay did not exist. A freshwater river maybe 200 feet wide snaked out to an ocean much farther offshore, when glaciers covered much of North America. “The ocean was 60 to 90 miles off the coast. Sea levels were about 390 feet lower back then,” said Kenneth Miller, a marine geologist at Rutgers University.
15,000 years ago
The head of the tide reached what today is the mouth of the Delaware Bay.
15,000-12,000 years ago
With seas still 40 meters, or 131 feet, lower than today, the saltwater extended about 18 miles up the ancestral Delaware River.
10,000 years ago
The mouth of the bay was about 3 miles wide, compared with 16 miles wide today, but seas were still 98 feet lower. This followed a rapid rise in sea level. Miller said seas rose 40 millimeters per year between 13,000 and 10,000 years ago. “It was 10 times what Atlantic City is seeing today, due to melting of the largest ice sheets in North America, Scandinavia and East Antarctica. It was almost entirely ice sheet melt,” he said.
Stewart Farrell, a coastal geologist at The Richard Stockton College of New Jersey, would love to see what the ancestral Delaware River looked like during the rapid melt-off. “It was like the Colorado River. All that ice melting off in the summer. The flow raged July through September and nothing in the winter, no flow, because it was frozen. It must have been awesome,” he said.
7,000-8,000 years ago
With seas 65 feet lower than today, the mouth of the bay was 6 miles wide. More salt water was coming in, and prevailing northwest winds pushed the water toward the lands that would be New Jersey.
5,000 years ago to now
With seas about 32 feet lower than today, about 60 percent of the bay existed. High points turned into islands, then shoals. Lands forested during the warming trend were submerged. Then it suddenly slowed. From the beginning of the Common Era to 1900, the seas increased by only 1 millimeter per year, Miller said, although the rate was 2 millimeters in Atlantic City due to subsidence.
The trend does not bode well for bayfront residents. The tide has risen on average almost 6 millimeters per year for 20,000 years. Even at the current rate of 4 millimeters per year, this would add 1 meter, or almost 40 inches, in the next 250 years. Greenhouse gases could make the increase even higher.