Spread a thin, even layer of the softened cream cheese completely to the edges of 18 pumpernickel bread slices.

Lay the slices of smoked salmon smoothly over the cream cheese layer. Using a very sharp chef's knife, trim the crusts and edges to form mathematically perfect squares.

On a cutting board, combine the minced red onion, capers, fresh dill, parsley, and lemon zest. Run your knife through the mixture repeatedly to create a fine, unified caper gremolata.

Sprinkle a pinch of this sharp, acidic gremolata evenly over the top of each smoked salmon square.

Place the thawed, dried salad shrimp into the bowl of a food processor.

Add the mayonnaise, sour cream, fresh lemon juice, diced celery, green onions, and parsley.

Pulse the machine repeatedly until the ingredients break down and unify into a smooth, thick, spreadable paste. Taste and season aggressively with the kosher salt and coarse black pepper.

Spread the shrimp paste in a thick, even layer onto the remaining 18 slices of pumpernickel bread.

Using a sharp knife, trim the edges to form perfect squares that identically match the dimensions of the salmon pieces.

Using a small spoon (preferably mother-of-pearl or bone to protect the flavor), gently place a precise dollop of caviar in the absolute center of each shrimp square.

On a large, flat serving platter, alternate the salmon squares and the shrimp squares to build a striking, geometric checkerboard pattern.

Garnish the outer edges of the platter with thinly sliced lemon wheels and sprigs of fresh dill before serving immediately.