Absolutely nothing will happen billions of gallons of freshwater goes into the sea all around the world each day.
All the rivers in each country flow into the sea and it's all freshwater and has done for millennium. So why the fixation of an Antarctic big lump of ice that broke away from the Continent?? Which happens every few years or so give or take a year. Admittedly this one is a little bigger
1987, Iceberg B-9, 5,390 km2 (2,080 sq mi)
1998, Iceberg A-38, about 6,900 km2 (2,700 sq mi)
1999, Iceberg B-17B 140 km2 (54 sq mi), shipping alert issued December 2009
2000, Iceberg B-15 11,000 km2 (4,200 sq mi)
2002, Iceberg C-19, 5,500 km2 (2,100 sq mi)
2002, Iceberg B-22, 5,490 km2 (2,120 sq mi)
2003 broke off, Iceberg B-15A, 3,100 km2 (1,200 sq mi)
2006, Iceberg D-16, 310 km2 (120 sq mi)
2010, Ice sheet, 260 km2 (100 sq mi), broken off of Petermann Glacier in northern Greenland on August 5, 2010, considered to be the largest Arctic iceberg since 1962. About a month later, this iceberg split into two pieces upon crashing into Joe Island in the Nares Strait next to Greenland. In June 2011, large fragments of the Petermann Ice Islands were observed off the Labrador coast.
2014, Iceberg B-31, 615 km2 (237 sq mi), 2014
2017, Iceberg A-68, (Larsen C) 5,800 km2 (2,200 sq mi)
2018, Iceberg B-46, 225 km2 (87 sq mi)
2019, Iceberg D-28, 1,636 km2 (632 sq mi)
2021, Iceberg A-74 from the Brunt Ice Shelf, 1,270 km2 (490 sq mi)
2021, Iceberg A-76 from the Ronne Ice Shelf, 4,320 km2 (1,670 sq mi
How about the billions of gallons from those?
Here's a question if it turns out that all these gallons of freshwater melt and rivers are affecting the Ecosystems. How are we going to stop all the rivers in the world from LOL contaminating the sea? We can't, can we?