This talk is part of the ALLways Learning Series, which invites ALL members and members of our local community to join us for a free, casual lecture each Friday during the academic year (formerly Lunchtime Learning Series).

Abstract: Earth experienced at least six ice ages (“Glacials”), separated by warm intervals (“Interglacials”) during the last 2.5 million years. We only find evidence of the most recent ice age, called the “Wisconsinan” around Minas Basin. The Wisconsinan ice cap waxed and waned from 75,000 years BP, peaking 50,000 years ago when it was at least three kilometers thick over the centre of the North American continent and 1.5 km thick over Nova Scotia. Since the amount of water on earth is fixed, global sea level drops when ice caps expand and vice versa. As a result, during the Last Glacial Maximum (LGM) 18,000 years ago, global sea level stood 120m lower than today.  

Ice caps had retreated more or less to their present-day position by 10,000 years ago, the start of the current Interglacial period called the Holocene. That fast historic melting rate is comparable to what is happening today because of the massive amount of fossil fuel burning since the mid 1800s, which has caused global sea level to rise 1.5m in the last 150 years. Without humanity’s interference in the natural climate cycles, earth would again be cooling towards an ice age in about 50,000 years.  

When ice caps melted, water was returned to the oceans, causing sea level to rise. Around 8,500 years the rising sea began to flood the previously glaciated land, but the sea didn’t flood Minas Basin until about 3,600 years ago because a gravel barrier existed across Minas Channel during the early Holocene; it was breached by the ocean as the tide range increased. The Mi’qmaq lived here when that happened and one of their legends is testimony to those events.  

When early Minas Basin became connected to the Bay of Fundy, it changed from a lake to a tidal estuary. The distribution of modern sediments in Minas Basin is explained by its complex tidal current regime. The north shore of Minas Basin has steep sides with gravelly shorelines. Fast tidal currents enter the basin along this shore and only small amounts of fine sediment can settle. Cobequid Bay is a dead end, the tidal currents turn around and mix with the fresh water of the Shubenacadie and Salmon rivers, creating massive tidal sand bodies. The currents are slowest in the southern bight of Minas Basin, where the finest sediment settles out of suspension. Hence the original name of our town: Mud Creek.  

Biography: Dr Elisabeth Kosters is a retired earth scientist. She worked for government organizations and Academia in the Netherlands, the US and Canada. Her expertise is on sediments and sedimentary rocks and this led her to work on issues ranging from coastal sedimentation and protection to  strategic gas reserve estimates. 

Learn more on the Earth Science Society website.